A World War Two bomb exploded during construction work near a train station in the German city of Munich, injuring four people.

The old aircraft bomb explosion happened on Wednesday during a tunnel drilling close to the main station near Donnersberger Bridge, bringing rail traffic to a standstill. As a column of smoke rose into the sky, some local trains were evacuated while travel to and from Germany’s busiest station was suspended. 

The fire service said there was no damage to the tracks and service resumed by mid-afternoon, the Associated Press reported.

"There is no danger outside this area," police said.

Though unexploded wartime bombs are frequently found in Germany and prompt big evacuations, most are defused by experts without exploding, BBC News reported. 

"It has to be investigated why no-one spotted this bomb earlier," Bavarian Interior Minister Joachim Hermann told German media.

World War Two ended more than 70 years ago but there are still more than 2,000 tons of live bombs and munitions discovered each year in Germany, Reuters reported. 

This has not been the first unexpected explosion in Germany. 

In 2014, a construction worker was killed when his power shovel struck a buried bomb, and in 2010, three police explosives experts died while trying to defuse a bomb. 

There were similar incidents in 2015, 2012 and 1994 as well.