Coast guard and military vessels scoured Philippine seas on Monday in a desperate search for passengers missing from a pair of Christmas ferry tragedies, amid fears the death toll could surpass 50.

Coast guard spokesman Lieutenant Commander Armand Balilo said deep sea divers on Sunday found 12 bodies inside the Catalyn B, a wooden ferry that collided with a fishing vessel and sank near Manila on Christmas Eve.

Those bodies were in addition to four passengers already confirmed dead, while 11 others were still missing.

Balilo said rescuers had not given up hope of finding some survivors.

"We cannot shift to search and retrieval (of bodies) because we are still scouring the area for survivors and hoping to find some," he said in an interview on the ABS-CBN television network.

Nevertheless, the search had entered its fourth day, meaning hopes of finding anyone else alive were fading and as many as 27 people may eventually be confirmed dead from the Catalyn B disaster.

Accidents common

Meanwhile, rescuers were pressing on in a separate search south of Manila where another ferry, the MV Baleno-9, went down late Saturday.

The confirmed death toll from that accident so far is six, but 23 remain missing, said Balilo.

Balilo said calm weather was aiding the coast guard and navy in their search for survivors, but no one had been found alive today morning.

Shipping accidents are common in the Philippines and usually involve poorly maintained, overloaded ferries which form the backbone of travel between the archipelago's islands.

Ferry passenger numbers usually surge over the Christmas period with many people travelling home to visit relatives.

- AFP