(CNN) -- Rescue operations were under way in the North Sea after a container vessel collided Wednesday night with a car carrier, which had 24 people aboard when it started sinking, a spokesman for the Netherlands Coast Guard said Thursday.
The carrier Baltic Ace began sinking immediately after it collided with the container vessel at 7:15 p.m. (1:15 p.m. ET), 60 kilometers (32 miles) west of Rotterdam, said Coast Guard P.R. Manager Peter Verburg.
Thirteen crew members were rescued. Four were taken to Rotterdam Hospital, seven to the Koksijde Air Base near Ostend, Belgium, and two were still aboard another vessel, he said.
Those rescued were suffering from hypothermia and minor injuries, he said.
The nationality of the crew was not immediately known.
Various fishing boats, merchant vessels and at least three helicopters were searching for more survivors.
The Baltic Ace had been en route from Zeebrugge, Belgium, to Kotka, Finland; the container vessel was en route from Grangemouth, Britain, to Antwerp, Belgium.