Divers have been tying weights to bodies found in a ferry that capsized in the central Philippines last weekend to get them out of the vessel, a coast guard official said Thursday.

The sunken ferry is seen from a Philippine air force helicopter. (Bullit Marquez/Associated Press)

Coast guard Commodore Luis Tuason said bodies have floated to the top of submerged compartments inside the ferry and there seems to be no other way to pull them through narrow corridors.

Debris blocking passageways, poor visibility and strong undercurrents are among the difficulties facing about 100 divers, including U.S. frogmen.

The coast guard has resisted cutting holes in the side of the upside-down the vessel, MV Princess of the Stars, because it fears that might cause an oil leak.

It remains unclear how many of the 850-plus passengers and crew were trapped when the seven-storey vessel ran aground and flipped over at the height of Typhoon Fengshen.

Rough water kept rescue workers away until Tuesday.

The Philippines Coast Guard says the search for and recovery of bodies could take up to a month.

Only 56 survivors have been found, while 124 bodies have been recovered after washing ashore or being spotted floating in the sea, some in life-jackets, coast guard Cmdr. Danilo Avila said.

The ferry disaster could raise the typhoon's death toll to more than 1,300, with 329 people confirmed dead from flooding and landslides and more than 200 missing.

The vessel was sailing from the capital Manila to Cebu when it flipped over. Only its hull remains visible above the waves off Sibuyan Island.

With files from the Associated Press