Finland on Monday led one of the biggest counter-pollution drills on the Baltic Sea, involving 70 vessels in the exercise.

The drill simulates a collision between two vessels in Finnish waters at 21 nautical miles (39 kilometres) off Helsinki, with wind and currents moving 15,000 tonnes of crude oil towards Finland's southern coast.

The exercise is primarily aimed at testing the ability of 10 oil response vessels in dealing with the crisis. Other participating vessels contributed by putting in place a floating barrier against the spill.

"The Balex Delta operational response exercise is the largest maritime emergency and counter-pollution drill of its kind in the Baltic Sea area and one of the largest worldwide," said the Finnish environment ministry in a statement.

It ends Wednesday.