Media playback is unsupported on your device Media caption Jon Kay saw the first UK aid being sent from RAF Brize Norton

The UK is investigating reports a Briton was killed in the earthquake in Nepal, the foreign secretary has said.

Philip Hammond said at least 500 Britons had been accounted for but staff were contacting tour operators and hospitals to trace others.

An RAF plane carrying aid supplies and Army troops, including Gurkha engineers, is on its way to Nepal, ahead of UK TV appeals for donations.

More than 5,000 people died in Saturday's earthquake.

Mr Hammond said the Foreign Office had estimated there were between 500 to 1,000 British nationals in Nepal but there was "no single co-ordinated list".

Officials had assisted more than 250 British nationals and 583 "either have left the country or are not in the country or are accounted for and safe in the country", he said.

"We are urgently investigating unconfirmed reports of a non-UK resident British national having been killed and our teams on the ground will report back as soon as they have any further information on that."

The BBC is aware of about 28 British or Irish families who are still waiting to hear from relatives.

The Disasters Emergency Committee (DEC) - comprising the UK's leading aid agencies - will make the televised appeal for donations on the BBC, ITV, Channel 4, Channel 5 and Sky.

The appeal, fronted by Absolutely Fabulous star and Gurkha campaigner Joanna Lumley, is due to be broadcast on BBC One at 17:55 BST and 22:50, BBC Two at 20:00 and ITV at 18:51.

A website and donation line have already been launched.

Gurkhas on Everest

The Army's first Gurkha regiments were founded in Nepal in 1815 and recruits still come from the country. The Ministry of Defence says more Gurkhas are expected to be sent to Nepal following the departure of troops from Maidstone-based 36 Engineers from RAF Brize Norton in Oxfordshire.

Meanwhile, soldiers from the Royal Gurkha Rifles, based at Shorncliffe Barracks in Kent, who were on Mount Everest when an avalanche struck, are now trekking down the mountain, identifying and reporting British nationals on the way. Gurkhas from the Army's training base near Kathmandu are also assisting the local authorities.

Nepal has declared three days of national mourning for the victims of the 7.8-magnitude earthquake. Officials say the death toll has now passed 5,000, but could reach 10,000, and at least 8,000 were injured.

Eighteen of the dead were killed in avalanches on Mt Everest, the world's tallest peak.

The massive earthquake and several aftershocks has affected eight million people, more than a quarter of the country's population, the United Nations has said.

Image caption The British army Gurkha engineers left from RAF Brize Norton on the RAF C-17 transporter on Monday night

Image copyright PA Image caption The aid includes solar lanterns to provide lighting and a means of charging phones, radios and torches

The UK aid flight from RAF Brize Norton was commissioned by the Department for International Development (DfID) and left on Monday night.

The RAF C-17 plane has now landed in the Middle East to refuel. It is also carrying more than 1,700 solar lanterns to help families who have had to sleep outside because their homes have been demolished or through fear of further aftershocks.

An RAF Hercules aircraft carrying additional kit is preparing to leave the base later.

BBC defence correspondent Jonathan Beale said the MoD is also looking at other options to help the rescue and relief efforts, including sending helicopters.

'Hugely challenging'

The Department for International Development had earlier deployed a team of more than 60 search and rescue responders and medical experts to support the relief effort.

The team - made up of seven search and rescue crews, four search and rescue dogs, a medical support team and a hazardous materials specialist - is now in Nepal's stricken capital, Kathmandu.

Image copyright WILL OLIVER Image caption Rescue workers from UK charity SARAID (Search and Rescue Assistance in Disasters) have arrived in Kathmandu

Image copyright EPA Image caption The SARAID team quickly set to work in the Sundarijal area

Image copyright Getty Images Image caption The UN says about eight million people have been affected by the earthquake

The situation on the ground remains "highly challenging", the UK Foreign Office said.

Patchy mobile telephone and email communications have made it difficult to locate people and families have been appealing for loved ones to get in contact through online people finders.

The University of Leicester has paid tribute to a US medical student who died following an avalanche at the Mt Everest base camp.

Dr Marisa Eve Girawong had been part way through a postgraduate mountain medicine course.

Dr Peter Barry, from the university's department of infection, immunity and inflammation, said she was "a beautiful, intelligent, outgoing person who effortlessly got on with everyone".

'Huge outpouring'

Speaking on BBC Radio 4's Today programme, DEC chief executive Saleh Saeed said entire villages had been completely destroyed in some areas of Nepal.

He added: "It is urgent, of course, that we launch this appeal and we are sure that the great British public will donate and help."

Aid was "getting in" by road and plane, he said, but warned that he expected the death toll to rise in the coming days.

The UK government has promised to match the first £5m of public donations.

Downing Street has already given £5m to help people affected by the earthquake. It said it had released £3m to address immediate needs and that £2m would be given to the Red Cross.

The Foreign Office has released an emergency number - +44 (0) 207 008 0000 - for people worried about loved ones who may have been in the area at the time.

It advises against all but essential travel to Nepal.

Britons in a safe place have been advised to remain there until it is safe to leave, but those able to leave Nepal safely have been encouraged to do so.