Unexploded World War 2 bomb found near Berlin train station

BERLIN, Germany — Berlin's main rail hub was partially paralyzed on Wednesday as police defused a World War II bomb found less than a mile from the station.

The 220-pound explosive, dropped on the German capital by the Allies some 70 years ago, was discovered Tuesday on a construction site to the north of the Hauptbahnhof station.

As police planned to defuse it around early Wednesday afternoon, nearby streets were cordoned off, houses evacuated and as many as 50 trains halted or diverted.

"The detonator will be unscrewed with a tool," a police spokesman told Agence France-Presse, before adding – not reassuringly – that "the [engineers] are trained but if something goes wrong they're history, because they're directly next to the bomb."

More from GlobalPost: WW2-era bomb explodes in Munich (VIDEO)

It wouldn't be the first time: last August, a 550-pound American-made ordinance went off in the southern city of Munich after bomb disposal experts were unable to defuse it. The supposedly "controlled" explosion sent a fireball into the sky, shattered windows, started fires and left a crater in the middle of the road.

In 2010, meanwhile, three sappers died when a wartime bomb they were preparing to defuse suddenly exploded in central Goettingen.

Thousands of tons of unexploded munitions are unearthed in Germany each year, costing the government millions of euros to dispose of.

The shells are only getting more dangerous as they age and deteriorate, veteran bomb disposal expert Hans-Juergen Weise told the Spiegel, explaining that US-made bombs in particular have chemical detonators that are easily corroded over time.

"One day such bombs will be so sensitive that no one will be able to handle them," Weise said in a 2008 interview. "We may have to stop defusing them as soon as next year."