The blaze was finally brought under control, but a trail of diesel has been spilled across the sea.

Fireboats battling to extinguish a fire on the Panamanian-registered crude oil tanker New Diamond off Sri Lanka's eastern coast in September 4, 2020.
Fireboats battling to extinguish a fire on the Panamanian-registered crude oil tanker New Diamond off Sri Lanka's eastern coast in September 4, 2020. (Sri Lanka's Air Force / AFP)

A stricken oil tanker off Sri Lanka that has been on fire since last week has left a kilometre-long oil slick across the Indian Ocean.

The country's navy said on Wednesday it fears an environmental disaster of epic proportions if the tanker explodes.

A fire first erupted on board last Thursday and was thought to have been completely doused on Saturday, but reignited a day later.

READ MORE: Stricken oil tanker pushed away from Sri Lankan coast

Sri Lanka's navy said there were no flames or smoke from the New Diamond vessel, which is carrying 270,000 tonnes of crude oil and 1,700 tonnes of diesel.

The fresh fire was triggered on Sunday by strong winds that pushed the crippled tanker about 20km closer to Sri Lanka's eastern shores.

A powerful tug boat was used to bring the drifting ship back to a location 68km from land, the navy said.

The Indian Coast Guard (ICG) said it had deployed aircraft to spray chemical dispersants on the slick and mitigate the environmental impact.

The ICG also said it provided 2,200kg of dry chemical powder to the Sri Lankan air force to drop on the burning tanker on Tuesday as a fire retardant.

The blaze had weakened the structure of the Panamanian-registered 330-metre tanker and the vessel was slightly leaning to the left, the ICG said.

READ MORE: Environmental disaster beckons as fire engulfs oil tanker near Sri Lanka

Rescuers said the blaze had not reached the crude oil cargo. The diesel is thought to have leaked when the ship's fuel storage tanks ruptured and mixed with sea water that was pumped to douse the flames.

Sri Lanka's chief prosecutor, Dappula de Livera, told local marine authorities to pursue a claim for damages and order the owners to tow the tanker away from Sri Lankan waters.

The vessel first reported a fire while passing the country's east coast on Thursday after a boiler room explosion killed a Filipino crew member.

In July, Japanese bulk carrier MV Wakashio crashed into a reef in Mauritius, leaking more than 1,000 tonnes of oil into the island nation's pristine waters.

Source: AFP