Philippine rescuers searched the smouldering ruins of a burnt-out ferry on Thursday for any survivors or more victims of a fire that swept through the inter-island vessel killing 29 people, including a six-month-old baby, authorities said.

Investigators have yet to identify the cause of the fire that started at about 11pm (1500 GMT) on Wednesday off the southern island of Basilan when many passengers were asleep in air-conditioned cabins on the ferry's lower deck.

"I thought I was dreaming but when I opened my eyes it was dark and we were surrounded by smoke," Mina Nani, 46, a passenger on the MV Lady Mary Joy 3, told DZRH radio.

She said she survived by jumping off the vessel and sharing a floatation device with another passenger until they were rescued.

There were conflicting figures for the number of people on the ferry, which officials said was not overloaded. The coast guard said 225 people including 36 crew were rescued.

Eleven people, including three children, drowned after jumping off the burning ship, while 18 died in the blaze on board, Governor Hadjiman Hataman Salliman told DZRH.