Pirates have hijacked an oil tanker with eight Sri Lankan crew members on board, a Somali official says, in the first hijacking of a large commercial ship since 2012.

Key points: Hijack off Somalia's coast is first such attack on a merchant ship in five years

Hijack off Somalia's coast is first such attack on a merchant ship in five years Eight crew are believed on board the vessel, piracy expert says

Eight crew are believed on board the vessel, piracy expert says The European Union Naval Task Force says it is investigating the incident

The vessel, Aris 13, sent a distress call on Monday, turned off its tracking system and altered course for the Somali port town of Alula, according to John Steed of the aid group Oceans Beyond Piracy.

It had been carrying fuel from Djibouti to Somalia's capital, Mogadishu, he said.

The Sri Lankan Government said the ship had eight Sri Lankan crew on board and flew a flag from the Comoros islands.

"The pirates hijacked the oil tanker and they brought it near Alula," said Mohamud Ahmed Eynab, the district commissioner for Alula.

Pirates in the town confirmed they were expecting the ship.

Aris 13 is owned by Panama company Armi Shipping and managed by Aurora Ship Management in the United Arab Emirates, according to the Equasis shipping data website.

The ship was being monitored by the United Kingdom Maritime Trade Organisation (UKMTO), the head of the International Maritime Bureau Piracy Reporting Centre in Kuala Lumpur, Noel Choong, said.

A spokeswoman for the European Union Naval Force operation off Somalia, Flight Lieutenant Louise Tagg, confirmed that an incident involving an oil tanker had occurred and an investigation was underway.

An official based in the Middle East with knowledge of the incident said that no ransom demand had been made.

Mr Steed said the seizure was the first commercial pirate attack off Somalia in five years.

Piracy off Somalia's coast was once a serious threat to the global shipping industry.

At least 237 attacks were carried out by pirates off the coast of Somalia in 2011, according to the International Maritime Bureau.

But attacks fell sharply after ship owners tightened security and avoided the Somali coast.

Intervention by regional naval forces that flooded into the area helped disrupt several hijack bids and improved security for the strategic trade route that leads through the Suez Canal and links the oilfields of the Middle East with European ports.

Reuters/AP