A ferry carrying about 100 passengers has sunk near Turkey's northwest port of Bandirma, killing at least one person and leaving four missing, officials say.

The ferry, which was also loaded with 73 lorries and two cars, went down in the Sea of Marmara shortly after leaving for Istanbul at 20:15GMT on Sunday.

Local fishermen joined five coastguard vessels, a helicopter and divers in rescue operations early on Monday.

Officials said 90 people had been rescued and that 31 of them were injured and being treated in hospitals.

"Our rescue operations are continuing [for the missing people] around the area where the boat sank, but because of the darkness of night it's been difficult to work," Selahattin Hatipoglu, governor of Balikesir province, said.

The cause of the sinking was not immediately known.

Passengers said the ship sank in about 15 minutes and that many of those on board were asleep in their vehicles when it began to go down.

"The ship was rocking back and forth, to the left then to the right, then finally sunk, completely sunk," according to one survivor.