The driver of the car involved in the collision in Central Java province did not see the oncoming train on a level crossing due to thick fog, local traffic officer Eko Ari Kisworo said in a statement issued by the police.
The train then collided with the car, which carried nine people and was flung about 20m (66ft) before hitting a pole and flipping into a rice field, Eko said.
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Four passengers, including a two-year-old girl and another who was 10, were killed, while the driver and the remaining passengers were injured, the officer added.
The accident came just days after a long-distance train slammed into the last, women-only carriage of a stationary commuter train near the Bekasi Timur station in West Java on Monday, killing 16 women and injuring at least 90 people.

President Prabowo Subianto has blamed that incident on unsafe level crossings and ordered a countrywide upgrade with guard posts or flyovers.

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