Sudden floods triggered by heavy rains have killed more than 400 people across parts of Pakistan, India-administered Kashmir and Nepal, authorities have said, with scores of people still missing.

In Pakistan, a helicopter carrying relief supplies to the flood-hit northwestern Bajaur region crashed due to bad weather, killing all five people on board, including two pilots, a government statement said.

Officials say flash floods triggered by torrential rains have killed over 280 people in India and Pakistan and left scores of others missing.