Pope Francis has led prayers for the victims of the earthquake in Nepal, which left more than 3,600 people dead after striking the south Asian nation on Saturday.

"I wish to express my closeness to the populations struck by a powerful earthquake in Nepal and in neighbouring countries," Francis told those gathered in St Peter's Square.

"I pray for the victims, for the wounded, and for all those who suffer because of this calamity. May they be sustained by fraternal solidarity."

On Saturday, a telegram was sent to the Bishop of the Apostolic Vicariate of Nepal, Paul Simick, on behalf of the Pope.

It said that the pontiff was deeply saddened to hear of the catastrophe, and that he "commends the souls of the victims to the long mercy of the Almighty".

According to Nepal's National Emergency Operation Centre, the current death toll stands at 3,617, with more than 6,500 wounded. Dozens more are reported to have been killed in neighbouring Tibet and India, the BBC reports, and it is feared that the number will continue to rise.

It is the worst earthquake to hit Nepal since 1934, when 8,500 people were killed.

The international community has rushed to respond to the crisis. The US has sent a military aircraft with 70 personnel to help with the rescue and relief effort, while specialty search-and-rescue teams are also being sent from Britain, Australia and New Zealand.

Mission agencies are also already at work to help victims, including the Red Cross, Christian Aid, Oxfam, Doctors Without Borders, Tearfund and the Church Mission Society. Many of them have been struggling to account for their staff on the ground, however, and Tearfund's head of humanitarian Support, Oenone Chadburn, said on Sunday that it was a "worst-case scenario quake".

"Some of these communities are unlikely to be accessed for a week, with landslides also a risk. A slide could affect the course of rivers, creating floods and posing huge additional risk to Bihar, India's poorest state," he explained.

"We are preparing a response team for travel, and establishing contact with staff and partners in the country. Our work will see us go out of our way to find difficult and remote locations – as part of our call to follow Jesus to the places of very greatest need. However, this brings a whole set of challenges."

Rural areas were hit particularly hard, Christian Aid's regional emergency manager, Ram Kishan, confirmed. He said that the most urgent need is for emergency shelter, clean water food, warm clothing and hygiene kits.

"The provision of civic and essential services in Nepal is weak, and hospitals and other medical services are under strain," he added.

A senior official in Gorkha district, the epicentre of the 7.9 magnetite quake, told the Associated Press that in some places, 70 per cent of houses had been destroyed. Initial estimates suggest that the cost of restructure will surpass $5 billion.