Two old-fashioned steam trains have collided in Germany's Radebeul, Saxony, leaving some 52 people injured, four of whom are in critical conditions.

The locomotives were taking about 250 enthusiasts on a trip to mark the local railway's 125th anniversary, when the incident happened.

An investigation was launched into the cause of the collision as work began on Sunday to pull the wreckage of the historical trains off the tracks, near Dresden.

More trains were operating during the anniversary than they usually do -- a factor that could have contributed to the incident. However, police said that the cause of the crash was not known yet.

"The reasons are not clear at the moment, we know that four people were injured seriously," Police spokesman Joerg Weyand was quoted by Reuters as saying. "We cannot say if human error or technical failure caused the crash," he added.

Seven children under the age of ten were among those injured, police said. Following the incident, festival organizers cancelled the rest of the event.

MMN/SME/MMA