Denmark’s National Maritime Authority issued a warning on Thursday for ships to avoid sailing through a key part of the Great Belt strait, one of the world’s busiest sea lanes, due to a risk of “falling missile fragments”.

The Great Belt strait is the main maritime access to the Baltic Sea. A naval exercise was ongoing in the area.

“The problem occurred during a mandatory test where the missile launcher is activated and cannot be deactivated,” the military said in a statement.

“Until the missile launcher is deactivated, there is a risk that the missile can fire and fly a few kilometres away,” the military added.

A naval exercise was ongoing in the area, a navigational warning showed.

The warning covered an area some four kilometres (2.5 miles) south of the Great Belt bridge, which crosses the strait. The bridge remained open to traffic, its operator said.

Updates to follow