The Disaster Management Centre (DMC) said the death toll had risen to 334, up from 212 earlier on Sunday, with nearly 400 missing and more than 1.3 million people across the island affected by the record rains.

The losses and damage are the worst since the devastating 2004 Asian tsunami that killed around 31,000 people and left more than a million homeless.

Rain had subsided across Sri Lanka but low-lying areas of the capital were flooded on Sunday and authorities were bracing for a major relief operation.

A Bell 212 helicopter carrying food for patients stranded at a hospital just north of Colombo crashed into a river on Sunday evening. An Air Force spokesman told AFP all five crew members were rescued and taken to a nearby hospital.

Another helicopter sent from India rescued 24 people on Sunday, including a pregnant woman and a man in a wheelchair, marooned in the central town of Kotmale, about 90 kilometres (55 miles) northeast of Colombo.

Pakistan was also sending rescue teams, the Sri Lankan Air Force said, while Japan will also send a team to assess Sri Lanka’s immediate needs and has pledged assistance.