Hundreds of people were unaccounted for early Wednesday after a ferry near South Korea sank, killing at least four people.

A passenger, rescued from the wreck, told The Associated Press he thinks many people were trapped inside the ship as it sunk. All together there were 459 people on board, many of them students.

Authorities announced at about 9 p.m. last night that 368 passengers had been rescued however just a few hours later, they recanted due to an error in counting and only 164 were confirmed alive.

The national Yonhap news agency reported that passengers were told to jump overboard wearing life jackets.

One witness told YTN television there was a "loud impact and noise" before the ferry started to sink.

A government official told Reuters that aircraft were deployed to search, along with Navy divers.

Local reports indicated that many students were on the Sewol and were headed to the island of Jeju for a school trip.

Reuters reported that heavy fog had set in off the west coast during the night which lead to the cancellation of several island ferry services.

The ferry did send a distress call Wednesday morning local time, confirmed the Busan Regional Maritime Affairs and Port Administration.

The model of the sunken ship is at capacity with a tally of around 900 people, and according to shipping records it was built in Japan in the mid-90's.