The army said on its website that three conscripts died and another four were injured in the accident in the Raseborg area at around 8 am (local time).
Police said on Twitter that one train passenger had also died and many more were injured.
Local media reported that the army vehicle, which was left a tangled wreck in a snow-covered forest, was taking part in a military excercise at the time.
Eleven people were taken to two hospitals in the region, Finnish news agency STT said.
In Finland, the last serious accident was in 1998 when a train travelling at more than 100 kilometres (60 miles) an hour derailed in Jyvaskyla in central Finland, killing 11 people and injuring 39.
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)