The Philippine ferry sank off the country's eastern coast on Thursday after being caught in a heavy storm and choppy waters, coast guards said.

Officials said that at least four passengers had died in the accident, while between 40 and 88 remained unaccounted for, according to varying media reports. The remaining passengers had been rescued.

"We also heard reports that there were casualties but we have not yet been able to validate this," said Armand Balilo, a spokesman for the Philippine coast guard. "Our concern now is to ensure that all rescued are in good condition."

Balilo said that army helicopters were rushing to the vicinity of Polilio Island, the ferry's destination and the area where it capsized, to rescue as many passengers as possible before nightfall.

Survivors tell of experience

Those who were rescued were taken to the nearby Dinahican village in Infanta, where disaster response teams were preparing clothes, food, water and medicine.

"About one hour after we left port, huge waves began to batter the ferry," Donel Jade Mendiola, one of the rescued passengers, told local radio station DZMM.  "The boat started to take in water in front and the passengers rushed to the side," he said, adding that he thought there were elderly people among the dead.

There are fears, however, that the death toll may still rise as bad weather conditions could hamper rescue efforts. One rescue helicopter was reportedly grounded due to the rough winds.

Pounding storms and choppy seas are common in the region. A new tropical storm packing sustained winds of up to 80 kilometers (50 miles) per hour is expected to make landfall on the nearby island of Mindanao by Friday morning, with storms and strong winds also set to hit the mainland.

The Philippines is also the site of the world's worst ever peacetime maritime accident, when in 1987 a passenger ferry collided with an oil tanker, killing over 4,300 people.

dm/jil (Reuters, dpa)