Police say a petrol bomb was thrown through a window at an asylum-seekers' home in a town in northwestern Germany, starting a small fire but injuring none of the residents.

Police spokesman Jens Petersen told the dpa news agency Friday that a mattress and a rug caught fire in the attack overnight on the school building in Salzhemmendorf that had been converted to house some 30 asylum seekers. The blaze was quickly extinguished.

Petersen says a woman and her three young children sleeping in a room next to the fire were unharmed. Police are looking for a car seen leaving the area around the time of the attack.

Germany has been largely welcoming to the massive influx of migrants this year, but attacks on them and shelters have also increased.