Updated 1.55pm

A tanker carrying 750 tonnes of diesel fuel from Egypt to Malta sank Saturday in the Gulf of Gabes off Tunisia's southeast coast, a spokesman for a local court said.

"The ship sank this morning in Tunisian territorial waters. For the moment, there is no leak," Mohamed Karray said, adding that a "disaster prevention committee will meet to decide on the measures to be taken".

The Equatorial Guinea-flagged Xelo was headed from the Egyptian port of Damietta to Malta when it requested entry to Tunisian waters on Friday evening due to bad weather.

It began taking water around seven kilometres (over four miles) offshore in the Gulf of Gabes and the engine room was engulfed, according to a Tunisian environment ministry statement.

A video published by Tunisia's Radio Carthage showed grainy footage of a vessel with the name 'Xelo' on its hull sinking beneath the waves. 

Tunisia's environment ministry said Tunisian authorities evacuated the seven-member crew and that the ship "risks leaking". 

Karray said the Georgian captain, four Turks and two Azerbaijanis were briefly hospitalised for checks and were now in a hotel.

The defence, interior, transport and customs ministries were working to avoid "a marine environmental disaster in the region and limit its impact", the environment ministry said.

Risk to Malta 'quite low' - marine biologist

The sinking prompted concerns about the potential ecological impact on Malta, should the Xelo's fuel load spill into the Mediterranean. 

Marine biologist Alan Deidun told Times of Malta, however, that the risk to Malta is relatively low even if the diesel spills into the sea.

This, he said, was primarily due to the sheer distance between Tunisia and Malta. 

“The vessel appears to be just off the Tunisian shore, that is roughly some 250 to 300km from Malta,” he said. “That is far enough for a spill of that size to disperse.” 

Deidun also said that it was good news that the ship was carrying diesel, rather than denser crude oil.  

Diesel is a relatively light fuel product when compared to crude oil and heavy fuel oil. The light fraction, or weight, of the fuel means it sits more easily on the sea's surface. 

Sources at Enemed, the state entity which buys fuel from shipping suppliers such as this, said there was no record of them expecting a transfer from this vessel.

They said it was likely that the vessel was on its way to the Eastern Mediterranean and had indicated Malta as its final destination with the intention of dropping anchor at a shallow sandy embankment off the island’s southern shore.