PRAGUE – A fire broke out in a restaurant in northern Czech Republic, killing six people and leaving six others with serious injuries, officials said Sunday.

Firefighters said the U Kojota restaurant in the city of Most, some 100 kilometers (63 miles) north of Prague, was still open when the fire started before midnight Saturday. Police and firefighters said the likely cause was a gas heater that overturned.

It took more than 60 firefighters until 1 a.m. to get the fire under control. The injured were treated in hospitals in Most and nearby cities. An investigation was underway.

Interior Minister Vit Rakusan, who visited the site Sunday morning, said some 30 people were evacuated from the restaurant and a nearby apartment house.

Most Mayor Marek Hrvol said it was the worst such tragedy in the city’s recent history.