Pope 'deeply saddened' by massive loss of life, expresses solidarity with those affected.
As the death toll passed 2,400, the US together with several European and Asian nations sent emergency crews to reinforce those scrambling to find survivors in the devastated capital, Kathmandu, and rural areas cut off by blocked roads and patchy phone networks.
"Roads have been damaged or blocked by landslides and communication lines are down, preventing us from reaching local Red Cross branches to get accurate information," said Jagan Chapagain, Asia Pacific director of the International Federation of the Red Cross and Red Crescent Societies (IFRC).
The IFRC said it was extremely concerned about the fate of rural villages close to the epicenter of the quake, some 80 kilometers from Kathmandu.
"We anticipate that there will be considerable destruction and loss of life," Chapaign added.
Other aid organizations responding to the emergency also struggled to assess requirements across the nation, and spoke of the fearsome effects of the quake.
"We witnessed terrible scenes of destruction — hospitals were evacuated with patients being treated on the ground outside, homes and buildings demolished and some roads cracked wide open," said Eleanor Trinchera, Caritas Australia Program Coordinator for Nepal.
Survivors slept in the open in Kathmandu overnight, braving the cold for fear of being crushed by the teetering ruins of buildings.
Hundreds of structures, including office blocks and a landmark nine-storey tower, crashed to the ground at around midday on Saturday when the 7.8-magnitude quake struck.
Meanwhile snowfalls on Saturday thwarted efforts to airlift survivors from an avalanche that hit part of Everest base camp, killing at least 17 people, although choppers started landing on Sunday.
Pope Francis said he was "deeply saddened" Saturday after hearing of the tragedy and expressed his solidarity with those affected.
The pontiff's feelings were expressed in a telegram sent by his Secretary of State Pietro Parolin to the Nepalese Catholic authorities.
"He expresses his solidarity with all affected by this disaster and assures those who grieve for deceased family members of his closeness in prayer," the statement read.
The pontiff also "offers encouragement to the civil authorities and emergency personnel as they continue their rescue efforts and assistance to those touched by this tragedy".
Secretary of State John Kerry said the United States was working closely with the Nepal government to provide assistance.
"To the people in Nepal and the region affected by this tragedy we send our heartfelt sympathies," he said.
A US disaster response team was en route to Nepal and an initial US$1 million in aid to address immediate needs had been authorized, the US Agency for International Development said.
Neighboring India dispatched two military transport planes to help with the rescue and relief efforts as it emerged that at least 47 people had died there from the effects of the massive quake.
There were similar offers from around the region, including Sri Lanka, Pakistan and, further afield, Japan.
China said it had dispatched a 62-member search and rescue team with sniffer dogs and had started work on an emergency humanitarian aid plan, state news agency Xinhua reported.
Chinese state media said 17 people had also been killed by the earthquake in Tibet.
'Urgent need' for assistance
Germany, Britain and Spain also pledged support and assistance, with Norway promising to provide 30 million krone ($3.9 million) in humanitarian aid.
British Prime Minister David Cameron said the earthquake was "shocking news" and vowed his country, which swiftly sent a team of humanitarian experts to Nepal, "will do all we can to help those caught up in it."
Israel also said it was sending an aid delegation to Nepal, including a team of paramedics and doctors.
Charity Christian Aid launched an appeal for funds and said it was working with partner agencies to reach the worst hit areas.
"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," said the group's regional emergency manager Ram Kishan in a statement.