An oil tanker which ran aground off the coast of Pakistan has broken into two.
The tanker, which was carrying 67,000 tonnes of crude oil, broke apart when the tide changed.
A thick layer of crude oil covers much of the Karachi coastline
Port authorities say the worst of the spillage is over, but a large amount of crude oil remains on board the vessel.
A thick black layer of oil covers much of the coastline around the city of Karachi, causing major environmental concern.
Federal communications secretary Iftikhar Rashid told reporters the worst was over.
"All possible oil spillage and all possible damage is done. The situation is not that bad."
He said the authorities would now start working to stabilise the ship.
On Tuesday, an emergency was declared along the Karachi coast as authorities admitted the leakage was damaging marine life.
Residents near the sea have also been complaining of feeling unwell.
Oil clean-up experts have arrived in the city, and India has offered to help deal with the spill as a goodwill gesture.
A government spokesman in Delhi said pollution response equipment, dispersants and containment booms could be made available.
Pakistan has not yet responded to the offer.
Ahmed Saeed, a marine ecology expert at the International Union for Conservation of Nature (IUCN), says 16 kilometres (10 miles) of the Arabian Sea coast have already been polluted.
"We can see it spread all over. On the beach the oil is almost three times more than it was [on Wednesday] and we cannot see the natural colour of sand," he told the AFP news agency.
If the oil slick spreads westwards, he warned, the breeding grounds of two rare species of turtle - the Green Turtle and Olive Ridley - could come under threat.
The Greek tanker, the MV Tasman Spirit chartered by Pakistan's National Shipping Corporation, ran aground at low tide close to Karachi on 28 July.
Heavy seas have been hampering salvage efforts
A salvage operation was abandoned and the crew of the ship evacuated on Wednesday.
Senior officials admit they are not properly equipped to handle the potential environmental disaster, but say some preventive measures are being taken to minimise damage to the harbour.
The Pakistani navy has been put on alert to assist the authorities.
Paramilitary troops have also been called out to cordon off one of the main beaches near an upmarket residential district, which has been almost completely covered by a thick layer of oil.
Eyewitnesses say hundreds of fish and turtles are lying dead on the beaches.
And residents of Karachi are starting to complain of headaches and nausea linked to the spill.
Dr Wafay Shakir, a neurologist at a Karachi hospital, told the Associated Press that exposure to crude oil "may cause nausea, headaches and throat infections".
He added that long-term exposure to toxins could be more serious.
The authorities say they could not have done more to deal with the disaster, and that Karachi residents are not in danger.
An aircraft with chemicals to stem pollution is being flown in from Singapore. And a British ship with fire-fighting equipment has also been brought in as a precaution.