Grave fears are mounting for 35 Australians missing in Nepal after catastrophic flooding and landslides tore through the Himalayan border region, killing more than 250 people.

Frantic searches for survivors are continuing for at least 1500 people known to be missing, including hundreds of tourists in the area to take part in a sacred pilgrimage.

There has been no confirmation of West Australians caught in the tragedy as the names of missing Australians began being revealed on Thursday afternoon, with most from the eastern states.

Nepal’s police confirmed on Thursday afternoon the death toll had risen to 270, 66 people were in hospital and at least 1500 remained missing — including an 11-year-old and 14-year-old from the same Australian family.

The full cost of the catastrophe is not yet known.

It is already the deadliest disaster to hit Nepal since the 2015 earthquake that killed almost 9000 people.

Foreign Minister Penny Wong said the immediate priority for the Australian Government was finding the missing Australians.

“The loss of life and the scale of the destruction is devastating,” Ms Wong said.

“We understand these Australians are part of separate pilgrimage and tour groups.

“I think it is well known that people are not only going there for trekking but also for spiritual reasons, so you would anticipate that the foreign nationals who were in the region would have been there for a variety of those reasons.

“Our thoughts and condolences are with those who have lost loved ones and those whose loved ones are missing and to all affected by this disaster.”

Tour group Kailash Journey has confirmed six Australians are among their missing travel group. That is in addition to one missing Australian travelling with Kathmandu Holiday Tours and Travels, and 15 who were travelling with US-based tour group Himalayan Glacier Adventures.

That group includes the two Australian children, named as Aarush and Ashwin Muralitharan. It is believed they were with their parents.

Chitrak Sharma’s parents Umesh and Krishna were there too.

“I’m just trying to get in touch with my parents. I just want to know that they’re ok,” he said.

“I just want to hear their voice again. I just want to talk to them again. I want to see them again.”

All but one of the 15 Australians with Hilalayan Glacier Adventures are from NSW, including family of four Rishab Iyer, 23, Rudhra Sreesharan Iyer, 20, Sreedharan Iyer Iyer, 52 and Lakshmi Sreedharan Iyer, 50.

A family friend, Nisha Khadka, said on Facebook some from that family were last known to have been in Kathmandu before the disaster.

The family is desperately trying to establish their whereabouts.

“They were last known to be in Kathmandu before the flood,” Ms Khadka wrote.

“If anyone has seen them, has any information about their whereabouts, or has found them safe, please contact me as soon as possible.

“Please share this post widely so it can reach anyone who may have information.”

Western Sydney couple Venkatraman Balakrishnan and Chitra Venkatraman were also among the large Australian contingent, according to the ABC.

Their son told the broadcaster he last spoke with his parents when they were near the Nepalese border with Tibet.

Senator Wong said she had spoken directly with Australia’s ambassadors in Nepal and Beijing and instructed them to do “everything they are able to do to ascertain the whereabouts and welfare of any Australians”.

“I’m sure there are many Australians who are very concerned about friends or family who may be in this region. I would say to you at this stage access and information are very limited given the scale of disaster,” Senator Wong said.

“We will do our best to ascertain whatever information we can. We are urgently seeking to confirm the welfare and whereabouts of Australians, and we will be in touch with their loved ones as soon as we have any confirmed information that we can share.

“We are coordinating with the Nepalese Government, the UN, the Red Cross and other organisations on the humanitarian response.”

Additional DFAT personnel, including crisis-response staff, are now being sent to the region.

Western Australian Premier Roger Cook said he did not yet know whether any Western Australians were among those missing.

“Our thoughts go out to everyone,” he said.

“I don’t know if they’re Western Australians, but any Australian that’s caught in this situation, I think that impacts us all deeply.

“And of course, that country is now having to deal with a severe flood situation.”

A man from North Brisbane is also among the Australians still unaccounted for.

He is a member of the Non-Resident Nepali Association of Australia, according to the group’s treasurer Sambhu Gaishe.

In Perth, members of the Nepalese community are anxiously waiting for word from relatives caught in the disaster zone.

Nepali Association of WA president Navin Bhandari said the lack of communication and the remoteness of the affected areas were making it extremely difficult to establish the fate of loved ones.

“What we know is that a few of the community members, who have family who live in Nepal, have been affected,” he said.

“They have not been in contact since 9am yesterday.”

Mr Bhandari said a Perth friend had been unable to reach his brother-in-law, an engineer working on a hydro project in Rasua, one of the first regions struck by the deadly flash flood.

There was speculation workers could be trapped inside tunnels constructed for the hydro project.

“They believe the tunnel is not destroyed because the tunnel is underground,” he said.

“But the access to the tunnel is blocked.”

The scale of the devastation has also been witnessed first-hand by relatives of Perth residents.

Mr Bhandari said another family connected to Perth had watched as floodwaters ripped through the town of Nuwakot.

“My friend’s uncle’s family lives in the town of Nuwakot,” he said.

“What I’ve heard is, half of the family members were washed away in front of the other half.”

Mr Bhandari said the families did not wish to make any comment at this stage.

The disaster began after a wall of mud and rock collapsed into a river on Wednesday, unleashing devastating flooding along the Himalayan border.

Nepali migrant Kiran Thapa, 46, was working from his Sydney office on Wednesday afternoon when his wife called to tell him what had happened.

The couple immediately began trying to contact relatives in flood-ravaged Nuwakot District, along the Trishuli River, where homes and infrastructure have been badly damaged.

“I was so panicked,” Mr Thapa told AAP.

His family has since been located after moving to higher ground, away from the muddy water that inundated their homes, including his own.

But two daughters of his nephew, aged nine and seven, remain stranded in a town on the opposite side of the river, sheltering at their school.

“All the bridges (have) collapsed, so there’s no way of getting there,” he said.

“They’re being taken care of ... but still we cannot come and bring them on this side because the only way to get them back is by helicopter.”

Melbourne-based Shyam Rana has endured a similar wait, spending the night trying to contact family in Nepal.

He said conditions on the ground were chaotic, with the terrain making both rescue efforts and communications extraordinarily difficult.

“I’ve heard it’s hard to get any rescue emergency vehicles into the area because of the land,” Mr Rama said.

“It’s hard to land helicopters and it’s hard to get the cars, trucks and army vehicles into there.”

He is still waiting to hear from extended family near the disaster zone.

For Mr Thapa, the immediate crisis is only the beginning of a much longer nightmare.

His family, including his 83-year-old mother, could face weeks stranded by the destruction, while the paddy fields they depend on for food have been ruined.

He fears authorities could be forced to spend weeks on rescue operations before they can turn their attention to rebuilding.

“At the moment they are all in a defensive mode, but after a few weeks or so, when they come to the realisation that they’ve lost everything ... that may be very hard for them to digest,” he said.

The Nepali Army said 125 people, including 20 foreign nationals, had been rescued from Timure and Mailung in northern Nepal.

“Health care has been provided to 64 injured at the emergency treatment center including specialist doctor officer of Nepali Army in Trishuli,” a statement said.

“Land and air rescue, emergency treatment and relief materials distribution of the injured are underway coordinatedly.”

The Australian Travel Industry Association advised anyone with upcoming travel plans to Nepal and China not to reach out to their tour operator, because they were prioritising people caught up in the unfolding tragedy.

“Our thoughts are with everyone affected by this tragedy in Nepal and Tibet,” ATIA director Mira Yates said.

“Australian tour operators and travel agents are reaching out directly to their customers who may be caught up in it, to make sure they’re safe and supported.

“If you’ve got a trip booked and haven’t been personally affected, please sit tight while your tour operator or travel agent prioritises those immediately impacted.

“Your tour operator or travel agent will be in touch as soon as they can to assist with your booking.”