A World War II bomb exploded at a construction site next to a busy railway line in Munich on Wednesday, injuring three people, one of them seriously, German police said.

A column of smoke was seen rising from the site near the Donnersbergerbruecke station. The construction site run by Germany’s national railway is located on the approach to Munich’s central station, which is a bit over a kilometer (about a half-mile) to the east. Trains to and from that station, one of Germany’s busiest, were suspended.

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Unexploded bombs are still found frequently in Germany, even 76 years after the end of the war, and often during work on construction sites.

They are usually defused or disposed of in controlled explosions, a process that sometimes entails large-scale evacuations as a precaution.

Bavaria’s state interior minister, Joachim Herrmann, said the 250-kilogram (550-pound) bomb was found during drilling work, German news agency dpa reported.

It wasn’t immediately clear why it wasn’t discovered earlier; in general, sites in central Munich are scanned carefully for possible unexploded bombs.