Dutch marine rescue ships are seen during a rescue operation for seven missing crew members of a cargo ship which collided with another vessel and sank in the North Sea.

Rotterdam - Dutch rescue workers on Thursday resumed their grim search for seven crew members missing after their cargo ship sank in a busy North Sea shipping lane, but said there was little hope of finding survivors in the icy waters.

“There are still seven missing, we're now searching with planes and helicopters,” coastguard spokesman Peter Westenberg told AFP.

“We're currently only searching for bodies because the chance that anyone has survived is very small.” he said.

Rescuers, including the Dutch navy, on Wednesday plucked 13 survivors from the water after the Baltic Ace car carrier collided with the Corvus J container ship about 100km southwest of Rotterdam.

They also pulled four bodies from the water before suspending the search overnight.

The 148-metre Bahamas-registered Baltic Ace sank shortly afterwards, the coastguard said. The Corvus J was also damaged, but assisted in the search for missing crew.

Rescue efforts overnight were hampered by snow flurries and plummeting temperates as well as strong winds and waves of up to three metres.

“The water temperature is around seven degrees Celsius, not very warm,” another coastguard spokesman, Marcel Oldenburger, told AFP.

“Survival time depends on your clothes, if you're wearing a survival suit and a life jacket you can last a while but if you fall overboard wearing jeans then that's really not much.”

The shipping lane where the accident happened is one of the busiest in the North Sea and an important passing point for ships sailing into Rotterdam port, Europe's largest and the fifth-largest in the world.

Janusz Wolosz, second secretary at the Polish embassy in The Hague, told AFP that 11 of the 24 crew were Polish, of whom six have been saved, including the captain.

“One of the sailors has been taken to Erasmus hospital in Rotterdam in good condition and doctors said he might be out today,” Wolosz said.

Four Poles including the captain have been taken to hospital in Belgium and one is being treated on a rescue ship, he said, adding that five have “the status of missing”.

Oldenburger said the rest of the crew was made up of Filipinos, Bulgarians and Ukrainians.

The Philippines and Ukrainian embassies could not say how many of their nationals had been on board the Baltic Ace, while the Bulgarian embassy referred questions to Sofia.

“The police are trying to identify the bodies that have been found,” Oldenburger said. He could not say if the bodies had been pulled from the water wearing life vests.

Four of the survivors were flown to a hospital in Rotterdam, seven taken by rescue helicopter to a hospital in Belgium and two were treated on board a rescue ship.

The coastguard said all survivors were suffering from hypothermia.

The Baltic Ace was heading from Zeebrugge in Belgium to Kotka in Finland and the Cypriot-registered Corvus J from Grangemouth in Scotland to Antwerp in Belgium.

Rotterdam port spokesman Sjaak Poppe told AFP the collision would not affect shipping in and out of the port. - AFP