A South Korean passenger ferry, which sank in waters off the country's southwestern coast on Wednesday, was strongly believed to have been caused by a sudden turn in direction.

The sudden turn triggered vehicles and shipping containers to be tossed off their place before making the ship off balance, local media reported Thursday, quoting data tracking the vessel's positions.

The 6,825-ton passenger ship, "Sewol," made an abrupt turn at around 8:48 a.m. local time Wednesday, according to the automatic identification system (AIS) data offered by the South Korean Oceans and Fisheries Ministry.

Why the captain suddenly made the turn had yet to be known, but the change in direction was believed to have moved some 180 cars and trucks and over 1,100 tons of shipping containers on the deck of the ship to one side, driving the ship to lean to the port side gradually.

The Sewol ship reportedly tilted first, rolled over on the port side and capsized before being totally submerged in the waters at around 11:30 a.m. local time Wednesday. It took around two and a half hours until the ship sank.

The passenger ship, which sank off Jindo Island, near the southwestern tip of South Korea, was originally believed that it may have run aground as some rescued passengers said they heard a thumping sound on the bow before the ship sinks.

The banging sound was estimated to be a noise made when the vehicles and containers were out of their place and crashing each other.

At the first stage, the ferry was believed to have veered off course as it departed some two and a half hours later than scheduled due to a heavy fog, but the oceans ministry said the ship was not far off its intended route.