(CNN) -- A bulldozer struck what authorities believe was a World War II-era bomb in a western German town Friday afternoon, causing a blast that killed the bulldozer driver, injured 13 other people and damaged homes, police said.

The blast occurred at a rubble storage site in Euskirchen, Germany, about 30 kilometers (19 miles) southeast of Cologne, police spokesman Helmut Conrads said.

Information on why police suspected a World War II bomb wasn't immediately available, though the unearthing of such ordnance in Germany -- where unexploded Allied bombs still are being discovered decades after the conflict -- wouldn't be unusual.

Two people were critically injured in Friday's blast, and 11 others suffered minor injuries, Conrads said.

The explosion happened at site that was storing construction rubble destined for recycling, according to Conrads.

"We can be lucky this hasn't happened earlier," he said.

The blast damaged homes in a 400-meter radius around the explosion, Conrads said.

The presence of unexploded World War II ordnance in Germany is common enough that companies hire private bomb disposal teams to check that sites are safe when construction is planned.

Last April, authorities briefly evacuated hundreds of people from an area in central Berlin after a Russian-made aerial bomb weighing about 100 kilograms (220 pounds) was unearthed 2 meters from a train track. Bomb disposal experts safely disabled the device.

In August 2012, a 250-kilogram (550-pound) bomb was discovered in central Munich. It had to be detonated where it lay because the fuse was unstable; the explosion damaged nearby buildings.

In 2011, 45,000 residents were evacuated from the city of Koblenz, on the Rhine and Moselle rivers, as bomb squads dealt with two bombs and a military fog-producing device that were dropped by American and British warplanes in the last years of the war. One was a 1.8-metric ton British bomb that could have wiped out the city center, according to the local fire brigade.

Three members of a bomb disposal squad were killed in 2010 when the device they were trying to defuse in the German town Gottingen went off.

2011: WWII bombs defused allowing 45,000 evacuated residents to return

CNN's Diana Magnay, Stephanie Halasz and Laura Smith-Spark contributed to this report.