(CNN) An underground electrical vault exploded at a restaurant on Saturday in Huntington Beach, California, injuring five people.

A series of three explosions took place during an Oktoberfest celebration at the Old World restaurant, where firefighters initially responded to a report of an electrical fire, Huntington Beach Fire Battalion Chief Jeffrey Lopez said.

Two firefighters and two civilians were initially reported injured in the explosion. All of the injuries are minor, Lopez said.

A third civilian was reported injured Sunday with "moderate to severe injuries" and remains hospitalized, Lopez said.

The first explosion took place around 8:20 p.m. when firefighters "had just barely walked up to the area involved," Lopez said.

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