"We do not yet know the scope of the damage, but this could be one of the deadliest and most devastating earthquakes since the 1934 tremor which devastated Nepal and Bihar," said Jagan Chapagain, Asia/Pacific director of the International Federation of the Red Cross and Red Crescent Societies (IFRC).
The IFCR said it was extremely concerned about the fate of rural villages close to the epicentre of the quake, some 80 kilometres from the capital Kathmandu.
"We anticipate that there will be considerable destruction and loss of life."
Other aid organisations responding to the emergency also struggled to assess the needs with communications cut off around the Himalayan nation.
"Communication is currently very difficult. Telephone lines are down and the electricity has been cut off making charging mobile phones difficult," said Cecilia Keizer, Oxfam country director in Nepal.
"People are gathered in their thousands in open spaces and are scared as there have been several aftershocks," she added.
Nations around world have also reacted to the deadly 7.8 magnitude quake that rocked Nepal.
The United States is sending a disaster response team and has authorised an initial USD 1 million in aid to address immediate needs, the US Agency for International Development said.
The European Union also said its humanitarian experts were heading to the crisis areas.
"The full extent of the casualties and damage is still unknown but reports indicate they will likely be high, both in terms of loss of life, injuries and damage to cultural heritage," the EU statement said.
In Europe, Britain, Germany and Spain also pledged support and assistance, with Norway promising to provide 30 million krone (USD 3.9 million, 3.5 million euros) in humanitarian aid.
"It is now important to get an overview of what the needs are so that relief efforts can be brought in as quickly and efficiently as possible. The funds will be channelled through the UN system and NGOs," said Norwegian Foreign Minister Borge Brende in a statement.
