Manila  - A private salvage team on Monday surveyed a sunken ferry in the Philippines in a bid to remove a cargo of toxic pesticides that forced authorities to suspend efforts to retrieve hundreds of bodies trapped inside, the coast guard said.

Divers from the Philippine-based Subsea Services Inc inspected the capsized MV Princess of the Stars, with only its hull protruding from the sea off Sibuyan island in Romblon province, 300 kilometres south of Manila.

Philippine authorities suspended on Friday retrieval operations for hundreds of dead bodies believed trapped inside the ferry after they discovered that the ill-fated vessel was carrying 10 tons of endosulfan, a restricted pesticide.

The coast guard said 56 people survived the tragedy, while 250 bodies have been recovered. More than 500 other people who were aboard the sunken ferry are still missing and presumed dead.

Transportation Undersecretary Elena Bautista said more than 100 divers involved in the retrieval operations were undergoing medical check-ups in Manila for possible contamination by the pesticide.

Tests showed the water around the ferry was not contaminated by endosulfan, a pesticide used in pineapple plantations that can cause death or attack the central nervous system when ingested by humans.

The salvage divers were planning to bore holes into the hull of the sunken ferry to collect water samples to test if the deadly cargo has leaked.

If the water is cleared of contamination, the hull will be pried open to remove the toxic chemical contained in a 40-foot container.

The MV Princess of the Stars sank at the height of typhoon Fengshen on June 21. Aside from the ferry sinking, Fengshen also caused massive floodings, landslides and other accidents, killing 540 people with 41 still missing. (dpa)