ATHENS, March 1 (Reuters) - Sixteen people were killed and least 85 were injured after two trains collided head-on in Greece late on Tuesday, the fire brigade said, while the circumstances of the crash remained unclear.

A passenger train travelling from Athens to the northern city of Thessaloniki, and a cargo train from Thessaloniki to Larissa, collided outside the city of Larissa in central Greece, said the governor of the Thessaly region.

"The collision was very strong," governor Konstantinos Agorastos told SKAI TV, adding the first four carriages of the passenger train had derailed, while the first two carriages were "almost completely destroyed".

Agorastos said about 250 passengers were evacuated safely to Thessaloniki on buses.

Broadcaster SKAI showed footage of derailed carriages, badly damaged with broken windows and thick plumes of smoke, as well as debris strewn across the road. Rescue workers were seen carrying torches in carriages looking for trapped passengers.

"There was panic in the carriage, people were screaming," a young man who was evacuated to a nearby bridge told SKAI TV.

"It was like an earthquake," Angelos Tsiamouras, another passenger, told ERT.

In the early hours of Wednesday, rescue crews were still searching for survivors.

"The evacuation of passengers is under way in very difficult conditions given the severity of the collision of the two trains," fire brigade spokesperson Vassilis Varthakogiannis said in a televised address.

Local media reported about 350 people were travelling on the train.