Emergency crew gather at the explosion site near Donnersbergerbrücke railway station on Wednesday.
Berlin CNN  — 

Four people have been injured in an explosion caused by an old aircraft bomb near a busy train station in the German city of Munich, police said Wednesday.

The explosion happened after drilling during construction work near Donnersbergerbruecke station caused the bomb to go off, police said. By Wednesday afternoon, emergency services had left the scene and trains had resumed running.

The explosion was caused by an old aircraft bomb, Munich police press officer Carolin Schrott told CNN.

“There is no danger outside the immediate area,” police said.

No further information was available on the type of bomb involved but munitions dating back to World War II are not uncommon finds in Germany. More than 70 years after the end of the war, roughly 2,000 tons of live bombs and munitions are still discovered in the country each year, Reuters reported.

According to official estimates, some 15% of the World War II bombs did not explode, and in some cases are buried six meters (20 feet) below ground.

In June 2019, residents of Ahlbach, southern Germany, were awoken early one morning by a sudden blast that left a crater 33 feet (10 meters) wide and 13 feet (4 meters) deep in a cornfield. Police later said it was “almost certainly” caused by a World War II bomb.

Police defused an unexploded World War II bomb weighing 1,100 pounds (500 kg) in Berlin in April 2018, and in September 2019 almost 60,000 people were evacuated in Frankfurt after a 3,000-pound bomb was found.

CNN’s Chris Stern reported from Berlin and Stephanie Halasz from London.