Coastguard officials hope to begin pumping 3,500 tonnes of oil from the stricken ship MSC Napoli to prevent more fuel leaking into the sea.
Some 200 tonnes of oil have already leaked from the cargo vessel, which is beached off the Devon coast.
Officials said the fuel on board – which is still in the tanks – was their main concern.
The operation to remove the heavy fuel oil was expected to start at first light and could last two days.
The ship suffered structural damage during Thursday’s storms and was deliberately beached off Branscombe to stop it sinking in deep water.
It is sharply listing and there are fears it could capsize and break up at any time.
A sheen of oil eight kilometres (five miles) long is now on the sea surface.
The ship has lost some 200 containers overboard, including two holding “dangerous but low-risk” goods.
Despite warning to stay away from the containers dozens of people reportedly spent the night “salvaging” thousands of pounds worth of goods on the shoreline.
It is believed 200 tonnes is close to the maximum that will leak out of the ship’s engine room.
Maritime and Coastguard Agency spokesman Paul Coley said attempts to remove the oil still in the ship’s tanks would start as soon as possible.
“It’s the main concern. It’s very difficult to control, for the moment the fuel is still in the tanks,” he said.
3,500 tonnes of oil
The 62,000 tonne vessel was carrying 2,323 containers, 158 of which are classed as having potentially hazardous contents.
Of the 200 that have gone overboard, one contained battery acid and perfumes, and one small gas bottles for car airbags.
Mr Coley said these were “considered dangerous goods but for us they’re low-risk”.
Others housed a variety of goods including BMW motorbikes and car parts.
Not all of the containers have been found and some have broken up. Some may have sunk while others could be far out to sea.
Forms handed out
Police said they had drafted in extra officers as people searched the shore by torchlight for goods overnight.
Under the Merchant Shipping Act 1995 it is an offence for people to remove items from a wreck if they conceal or keep possession of cargo and refuse to surrender it, police said.
Officers handed forms to those searching the coast on which they must declare what items they have taken.
The ship was being towed to Portland Harbour in Dorset for a salvage operation, but on Friday coastguards decided to beach it because of its structural damage – a fracture on both sides.
An eight-person salvage team is on board, and a team of divers is being flown in to join them.
Environmental damage is so far said to be minimal. Three oil-covered birds have been found.
Residents in nearby Sidmouth have spoken of the concern about the leak.
One man told the BBC: “It’s a real worry that we could get pollution and there’s a lot of wildlife lives on these shores, and certain rare sea birds.”
Julian Wardlaw, of the Environment Agency, said: “We have an extremely sensitive bit of coastline; we are dealing with a World Heritage Site and we are working to make sure that damage is minimised.”
Meanwhile, it has emerged that the ship previously ran aground off Singapore in 2001.
It was previously named CMA-CGM Normandie and ran aground in the Strait of Malacca in 2001.
The ship subsequently had to undergo “major repairs” in Vietnam, according to Tore Hoifodt, senior vice president at DNV, which classes and inspects cargo ships.
People who may find a washed-up container are being asked to stay well clear and report it to Portland Coastguard on 01305 760439.