Low-flying search planes spotted three Filipino fishermen drifting at sea and flashing mirrors to signal for help, as authorities stepped up the search for 261 others missing more than a week after a typhoon killed hundreds in the southern Philippines.

Indonesia sent a ship to join the search for the fishermen, who may have been swept toward the Celebes Sea from the Pacific Ocean off southern Mindanao Island, said regional military spokesman Captain Severino David.

A total of 35 fishermen have been rescued in the past three days, including three found Tuesday (local time) in a small boat drifting about 255 kilometres east of Davao Oriental province, where the typhoon made landfall December 4, David said on Wednesday. 

Low-flying search planes spotted them and gave their locations to rescue ships. Although weak and dehydrated, some were still able to signal to the planes using mirrors, David said. 

''The typhoon caught up with them, and they may have lost their way and ran out of fuel,'' he said.

The more than 300 tuna fishermen were about 220 kilometres east of Davao Oriental province as early as October. Typhoon Bopha's top winds of 210 kilometres per hour apparently made it difficult for them to return to shore.

The storm killed at least 740 people, many as floods swept through mountainous southern towns of the archipelago. Nearly 900 people are missing, including the fishermen. Rescuers recovered at least four bodies from the sea and continued to find remains buried under mud and rubble in the worst-hit farming province of Compostela Valley and in flood-ravaged coastal towns. 

Regional coast guard Commodore George Ursabia said most of the missing fishermen worked for companies based in southern General Santos City, known as the tuna capital of the Philippines.

They sailed to fishing grounds in October after a fishing ban was lifted Sept. 30.

''I am still hoping that they are still alive,'' said Civil Defence chief Benito Ramos, citing the experience of a group of fishermen who survived in rough seas in the northern Philippines for 21 days following another storm.

He said at least some of the missing fishermen may have taken shelter in islands in the Celebes Sea.

The typhoon knocked out power, destroyed houses, uprooted trees and set off flash floods that washes away roads and bridges and entire communities.

Hundreds of thousands were left homeless, and the Philippine government launched a massive relief effort. The UN has appealed to donors for US$65 million in emergency humanitarian assistance.

- AP