MANILA, Philippines (1st UPDATE) - Philippine Coast Guard (PCG) 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.

Authorities said they had not given up hope of finding dozens of people still missing from the latest accidents to hit the archipelago's notoriously dangerous water-travel industry, but warned against expecting miracles.

Twenty-three people remain unaccounted for after a small inter-island ferry, the MV Baleno-9, sank off the southern coast of the Philippines' main Luzon island just before midnight on Saturday.

"The survivors said the ship went down in seconds and other people did not get out, so the missing bodies may still be inside," Maritime Industry Authority chief Maria Elena Bautista told reporters.

The official death toll from the MV Baleno-9 so far is six. About 60 other passengers who were on board the vessel were picked up by rescue boats and other ferries in the area near Batangas city.

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

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

"We cannot shift to search and retrieval (of bodies) because we are still scouring the area for survivors and hoping to find some," Balilo 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. As many as 27 people may eventually be confirmed dead from the Catalyn B accident.

Maritime disasters occur frequently in the Philippines and usually involve poorly maintained, overloaded ferries that form the backbone of travel between the archipelago's roughly 7,000 islands.

Christmas is a particularly dangerous time because millions of people in the Catholic nation travel to be with their families for the festive period.

The world's deadliest peacetime maritime disaster occurred south of Manila in December 1987 when a ferry carrying Christmas holidaymakers collided with a small oil tanker, killing more than 4,000 people.

The aftermath of the latest tragedies saw a familiar pattern with officials raising questions about a range of safety issues such as overcrowding, inaccurate manifests and ship crew not following correct procedures.

The MV Baleno-9 sank apparently without having collided with anything, and did not report any problems beforehand.

"We are... wondering why the captain did not make a distress call and about the accounts of the passengers that there was no order to abandon ship," Batangas coast guard chief Lieutenant Commander Troy Cornelio said.

Cornelio also said an official investigation would look into whether everyone on board was listed on the ferry's manifest.

In the meantime, Besta Lines, the owner of the MV Baleno-9, has had all its operations suspended, Cornelio said.

In reaction to the twin accidents, President Gloria Arroyo has ordered government agencies to conduct a safety audit of all shipping companies.

The government typically announces such audits after ferry accidents, apparently with little positive impact on the industry's safety procedures.