Six persons were killed Thursday in northeastern Poland after the van they were traveling crossed into oncoming traffic and was hit by a truck, the police said.

According to the Bialystok police spokesman, the van may have hit a slippery patch of the road it was traveling between the cities of Zambrow and Wysokie Mazowieckie, the AP reported.

The spokesman said that both vehicles ended up in a ditch and all six passengers of the van were killed instantly, while the truck driver sustained a hand injury.

The authorities are investigating the cause of the accident.