Eight people were also taken to hospital with burns and around 30 people were evacuated from the restaurant and a nearby building, the fire rescue service said.
The injured were treated in hospitals in Most and nearby cities.
Police and firefighters said the cause of the fire at the U Kojota restaurant was a gas heater that overturned.
The restaurant was still open when the fire started before midnight on Saturday, and it took more than 60 firefighters until 1 a.m. to get it under control.
Interior Minister Vit Rakusan visited the scene on Sunday morning
Most Mayor Marek Hrvol said it was the worst such tragedy in the city’s recent history.
