Fresh oil has begun pouring from a Turkish tanker that ran aground four years ago off the coast of Cape Town, South Africa's premier tourist destination, an official said on Wednesday.

An attempted controlled explosion damaged the vessel during clean-up operations, city disaster management spokesman Wilfred Solomons-Johannes said.

One of the tanks ruptured in the explosion "releasing oil that was onboard the wreck," Solomons-Johannes told the national Sapa news agency.

Conservation officials were monitoring the spill, which hadn't put the environment in immediate danger, he added.

This was the second spill from the wreck in a year.

In September, it leaked oil onto the city's beaches after breaking up into three pieces.

The Panamanian-registered and Turkish-operated ship was carrying 30,000 tonnes of coal and 600 tonnes of heavy fuel when it developed engine problems in September 2009 on its way to Gibraltar.