The Catholic Relief Service says it is already transporting emergency relief materials from India to Nepal to help families following the powerful quake which has left at least 700 people dead, although many estimates are higher.
It said it was working to get tents, shelter kits, water, sanitation and hygiene materials to people.
Dozens of people have also been injured in the capital city Kathmandu after the quake which hit at around noon local time, causing extensive damage to buildings.
On national radio leaders appealed for calm and warned people of aftershocks.
The Catholic Relief Service said on Twitter: "We are looking at overland transport options to get emergency relief materials to families, since the airport is closed.
"Our prayers are with everyone affected by the earthquake that struck Nepal today. Please keep them in your prayers."
Oenone Chadburn, Tearfund's Head of Humanitarian Support, said it was "likely to be our worst earthquake scenario: a perfect-storm disaster".
She added: "The geography – the mountainous roads – mean supplies will require air-lifting in, generating a massive cost in helping remote communities.
"It's 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.'
"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."
