Indian coastguards on Monday said that leaking oil from a stricken container ship that collided with another vessel off Mumbai had reduced to a trickle, but fears about its impact on the coastline remained.

Ships and aircraft involved in the clean-up operation reported "almost nil oil spill" from the MSC Chitra on Monday evening, officials said in a statement, two days after the collision.

Six coastguard ships have been battling choppy seas, monsoon rain and strong winds to contain what the country's shipping ministry described as a "heavy oil spillage" from the badly listing vessel's fuel tanks.

The Panamanian-registered ship was lying at a sharp 60-degree angle to its port side about five nautical miles off shore, with containers and other cargo falling into the murky water, an AFP photographer at the scene said.

The shipping ministry said 120 containers in all had fallen from the deck and an operation was under way to retrieve them.

Thirty-one containers on deck were loaded with "dangerous cargo" of corrosive, toxic and flammable materials.

"It is not clear whether these containers have also fallen off but considering that the vessel is almost heeled over, it would be fair to assume that these containers would fall off, if not already in water," it said.

The vessel was carrying 2,700 tonnes of fuel oil and 300 tonnes of diesel oil. Some 1,200 tonnes of fuel oil was in the ruptured tanks on the ship's port side, the ministry said.

The coastguard said in a statement: "The oil spill is a potential threat to the marine environment given its chemical characteristics, however as of now the situation is under control."

Broken patches of oil have been sighted on the water across the Arabian Sea from the landmark Gateway of India monument, including around the Elephanta Island World Heritage Site, but have now been cleared, it added.

Environmental emergency teams put on alert since the collision on Saturday said earlier they were analysing oil samples found on mainland beaches adjacent to Mumbai.

A coastguard helicopter has been dropping oil-dispersal spray on the slick.

Indian Prime Minister Manmohan Singh called for a report from the shipping ministry into the spill, while environment minister Jairam Ramesh told parliament that legal action had been launched against the ships' owners.

Fishing in the area has been suspended and Mumbai's port -- India's busiest for container vessels -- has been closed for the night.

A salvage operation is expected to begin only at the end of the month, when bad weather subsides, the shipping ministry said.

The MSC Chitra, which was laden with 1,219 containers, was leaving Mumbai when it was in a collision with the MV Khalijia-III, another Panamanian-registered ship, coming into port.

Both ships developed cracks in the incident and 33 crew members were rescued. But police said one of its officers drowned after he fell off a four-man speedboat patrolling the area around the stricken ship.

"The other three constables also could not rescue him as none of them, including the victim, knew swimming," a police spokesman said.

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