The fire in the town of Most, about seven miles northwest of Prague, broke out in connection with some form of gas explosion.
The incident is said to have occurred shortly after 10 pm on Saturday. The fire was not under control until midnight.
"The fire spread extremely quickly", the local rescue service reports in a Facebook post.
All six fatalities were found inside the restaurant. Of the eight injured, six are reported to have severe injuries.
Some of them have very severe injuries and are in critical condition, says regional rescue chief Petr Bures to Czech TV.
About 30 people were evacuated from the restaurant and nearby apartments.
The police believe it was an accident.
