Two cars of an express passenger train derailed and slammed into a parked freight train at a station, killing at least 33 people and injuring 15, the state Tanjug news agency reported today. One passenger was quoted as saying the express train entered the station in eastern Yugoslavia at high speed, then slammed on its breaks. But the news agency said the driver obeyed all signals while entering the station. The crash occurred at 7:20 p.m. Sunday in Lapovo, 50 miles south of Belgrade. Rescue teams worked through the night to reach the victims, using blow torches to cut through the derailed coaches, Tanjug said. The train was traveling from the southern city of Skoplje to Belgrade when its last two cars jumped off the rails at the Lapovo station and rammed into an engine of a parked freight train, Tanjug said. A Belgrade radio report described the impact as ``tremendous.'' Initial findings suggest that technical failure, rather than human error, was the cause of the accident as the driver of the passenger train reportedly entered the station observing all signals, the agency said. ``I felt the train arrived in the station at full speed before braking suddenly. We kept on sitting for 15 minutes without knowing what was going on,'' Merima Cvetkovic of Belgrade told the newspaper Politika. Citizens offered their private vehicles to help ambulances transport the injured to hospitals. The government of Serbia today asked federal authorities to proclaim Wednesday a day of national mourning for the victims, but there was no immediate word on whether the request was approved.