The minibus carrying 10 people, eight women and two men, drove on to the crossing near the city of Lodz. The force of the collision hurled the bus 30 metres down the track, a police officer said.
"The impact was so strong that we cannot even recognise the make of the vehicle," the officer, Krzysztof Zielinski, told broadcaster TVN 24. "None of the train passengers was hurt."
Eight people died at the scene of the accident, while a ninth person died later in hospital, a police spokesman said. One woman was being treated in hospital for serious injuries.
The crossing had a stop sign but no barrier or guards.
Most of the victims are from neighbouring Ukraine but their identities are still being checked, said Joanna Chelminska, governor of the Lodz region.
"I have already alerted the Ukrainian embassy, its consul or a deputy consul will probably come to the accident location," Chelminska told TVN 24.
In March, 16 people died and 60 were injured in a head-on collision between two trains in southern Poland.
