The United Nations said Friday it had received just $22 million of the $415 million it had appealed for in Nepal following the recent earthquake, and called for aid contributions to be "dramatically ramped up".

Jamie McGoldrick, UN resident coordinator for Nepal, warned of a race against time to deliver relief supplies to remote areas -- some of which are accessible only on foot -- before heavy monsoon rains arrive, expected in June.

Thousands have been affected by the devastating April 25 quake, and more than 7,800 killed.

"Of the requested $415 million to support immediate humanitarian interventions, only $22.4 million was received. This needs to be dramatically ramped up," McGoldrick told reporters in the capital Kathmandu.

"The relief needs remain great and we urgently need funds to be able to continue our work.

"We need to (deliver relief) urgently, so that people have roofs over their heads and their other urgent needs are addressed before the monsoon season starts," he said.

The 7.8-magnitude quake ripped through vast swathes of the impoverished Himalayan nation in Nepal's deadliest disaster in 80 years.

It destroyed close to 300,000 homes and injured almost 16,000 people. More than 100 were killed in India and China.

Paul Dillon, a project manager at the International Organization for Migration, urged the international community to dig deep.

"Someone has to open the tap," he told reporters in Kathmandu Friday. "We cannot run our responses on credit cards. Those who have offered help need to make good on their pledges."