At least 2,000 people are now known to have died in the 7.8 magnitude tremor which hit close to the capital Kathmandu.
Tens of thousands of people spent the night in the open amid fears of aftershocks that could bring down more buildings.
Modern houses and ancient temples toppled alongside each other as the ground shook at noon local time.
Christian Aid has launched an urgent appeal for support and its regional emergency manager, Ram Kishan, said: "Rural areas were hit particularly hard by the earthquake, but little information has so far emerged as travel is difficult, not least because of damaged infrastructure.
"We fear, therefore, that the death count could be much higher, as well as the loss of buildings and property.
"Our partners are en route to establish where need is greatest, so that we can respond quickly and effectively.
"It's clear from what has emerged so far that there is an urgent need for emergency shelters, food and clean drinking water, warm clothing, blankets and hygiene kits."
Christian charity World Vision has also launched an appeal and was urging prayers.
Its Country director for Nepal, Liz Satow, said: "Buildings and walls across Kathmandu have collapsed, although it is hard to tell how serious and extensive the damage is.
"We know that hundreds, of people have been killed and injured. Many people are too frightened to go into the buildings due to fear they will collapse with aftershocks."
World Vision staff visiting a local hospital said there had been an influx of injured patients and an increasing need to help manage the crowds of people requiring assistance.
The charity's Katherine Rose Yee said: "We were in the square when the earth shook. I was so scared that I thought I was going to die. I was shouting 'open space, open space' as we were rushed to safety."
Efforts are currently underway to try and reopen Kathmandu airport to make it easier to get vital aid into the country.
Catholic charity Caritas is also sending supplies and workers to the region.
It said many of its help would have to come by road from India because of the airport closure.
Nepal director Fr. Pius Perumana S.J. is in Kathmandu and said: "It was the worst earthquake I have ever experienced in my life. The aftershocks are still strong. The indications so far are that this is a major emergency.
He said that there has been lots of physical damage, electricity has been down making communications difficult and roads are blocked.
"Lots of houses have fallen down and there are lots with cracks. Thank God it was during the day and on a holiday as many people were outside when the quake happened," he added.
Sian Merrylees from Christian charity World Vision speaking to Premier's Antony Bushfield