The crowded ferry carrying 267 people capsized on Sunday about four nautical miles offshore shortly after leaving the port of Kyrenia in the north of the divided island.

Rescuers in the Turkish Republic of Northern Cyprus (TRNC), which is only recognised by Ankara, pulled 239 people to safety, but eight others died "and the search continues for 20 people," said prime minister Unal Ustal.

All eight people who died were citizens of Turkey, as well as 18 of those who are missing, according to TRNC authorities. The other two missing are from Northern Cyprus, they said.

Police detained the captain and 15 others.

Nine of them appeared in court in Kyrenia, known as Girne in Turkish, charged with negligent homicide, as Northern Cyprus began three days of mourning, the official TAK news agency said.

Addressing the court, the captain and crew said the front of the vessel had been smashed open by the force of the waves, Turkey's Anadolu state news agency said.

The captain was remanded in custody.

TRNC president Tufan Erhurman told reporters divers were trying to retrieve data from the vessel's so-called "black box" in order to understand what caused the deadly incident.

"Divers were deployed today... and this effort will continue tomorrow as well," he said, vowing "to get to the bottom of every aspect". He stressed that the ferry company "will certainly be held accountable".

"Definitive information will likely be provided tomorrow (on Tuesday) in the form of confirmed data," he said.

Khassim Diagne, the UN Secretary-General's representative in Cyprus, said he was "deeply saddened by the tragic loss of life" and extended his sincere condolences to the families affected.

- 'Fight for survival' -

Several survivors from the vessel, a French-made Filo Jet catamaran, said they heard what sounded like an explosion shortly before it capsized.

Passengers said the boat had begun taking on water, with the captain trying to return to port before the vessel capsized.

Footage from the scene broadcast by Turkish television showed the capsized ferry with passengers wearing life jackets sitting atop its orange hull.

Shortly afterwards, the ferry sank and is currently lying at a depth of 514 metres (1,686 feet), said the TRNC's transport minister, Erhan Arikli.

Some survivors said there was not enough safety equipment for all the passengers.

"Some people had to jump without lifebuoys or life jackets," one young man, Efe Multici, told CNN Turk. "It was literally a fight for survival."

One of the victims was a policeman who had returned to the catamaran to try to find life jackets for his wife and child, who survived, according to Turkish newspaper Sabah.

Turkey sent six naval vessels and two drones, among others, to help the rescue efforts on Sunday, which were also joined by private boats in the area.

The vessel was built around the 2000s by Iris Catamarans, a subsidiary of now-defunct French group Fountaine Pajot, company founder Jean-Francois Fountaine told AFP, saying he did not have any information on the accident.

Cyprus has been split since 1974, when Turkey invaded and occupied the northern third of the island in response to an Athens-engineered Greek Cypriot coup seeking unification with Greece.

Today the island comprises the TRNC, which declared independence in 1983 but is only recognised by Turkey, and the EU member Republic of Cyprus in the south.

The TRNC is served by regular air and sea links to Turkey.