BERLIN—Four people were injured after a decades-old bomb dropped from an aircraft in World War II exploded during construction works near the main train station in Munich on Wednesday, authorities said.

One of the people sustained heavy injuries from the explosion, which shook nearby windows and produced a large column of smoke.

The 550-pound...

BERLIN—Four people were injured after a decades-old bomb dropped from an aircraft in World War II exploded during construction works near the main train station in Munich on Wednesday, authorities said.

One of the people sustained heavy injuries from the explosion, which shook nearby windows and produced a large column of smoke.

The 550-pound aerial bomb was struck during drilling works and debris flew for hundreds of meters, according to Bavaria’s Interior Ministry.

More than 70 years after the end of World War II, unexploded bombs are still found frequently in Germany. An untold number of bombs, artillery shells and hand grenades from the war are still hiding underground around the country. Experts have estimated that the unexploded ordnance totals around 100,000 tons.

Several thousand bombs and other explosives are recovered every year. In most cases they are safely defused or disposed of.

Workers check the tracks after the explosion, which halted rail travel to and from the station.

Photo: christof stache/Agence France-Presse/Getty Images

Wartime bombs are often found during construction work. Rendering them safe sometimes requires controlled explosions, which can involve large-scale evacuations of residents in the surrounding area. Last year, more than 10,000 residents in Frankfurt were told to leave their homes after the discovery of a 1,100-pound bomb from World War II.

In 2010, three members of a bomb-disposal squad were killed and others wounded during an attempt to disarm an explosive device in the central German city of Göttingen.

After Wednesday’s explosion, rail travel to and from Munich’s train station, one of Germany’s busiest, was suspended. It wasn’t immediately clear why the bomb wasn’t discovered earlier, as building sites in Germany are usually checked in advance for unexploded ordnance, authorities said. Police said there was no indication of foul play.

Ordnance-disposal specialists were on site to examine the remains of the bomb, the local fire department said, adding that there was no ongoing danger to the population.

Write to Georgi Kantchev at georgi.kantchev@wsj.com