An oil tanker and a cargo ship collided in thick fog in the English Channel in what coastguards said was "a very serious incident".
Norwegian cargo vessel Starhurdla collided with the oil tanker Cape Bradley at 0715 GMT on Thursday, six miles off the French coast of Boulogne.
Dover Coastguard, which was called in to assist the rescue operation, said no-one was hurt and no oil had leaked.
But a spokesman said the incident had the potential to be far more serious.
Inquiry under way
"It could have been very serious because of the high flashpoint cargo," said Mike Painter.
A tug was used to tow the Starhurdla into Boulogne after the crew reported taking on water.
The Cape Bradley only sustained minor damage and was escorted into Rotterdam, Holland.
An inquiry into the collision is under way.