A broken gas pipe spewed flames when a restaurant was torched in a late-night arson.
Firefighters spent an hour tackling the blaze in Worthing after a mains broke and caused an explosion.
The fire is thought to have caused damage worth tens of thousands of pounds.
Detectives are trying to establish whether the gas supply was tampered with deliberately to help the blaze spread, or if it was damaged by a fire that had already started.
The fire took hold at Beach House Park Cafe, formerly Bogarts, in Lyndhurst Road, Worthing, shortly after 10pm on Saturday.
The restaurant was closed at the time.
Flames were leaping from the windows when fire crews arrived, being fed by a break in an outdoor gas pipe.
Firefighters believe the source of the fire may have been a wheelie bin pushed against the back of the building.
Nearly half the 30m x 15m building was damaged by smoke or flames.
Youths who were in the area at the time are understood to have reported seeing suspicious behaviour at the restaurant.
Detective Inspector Dave Wilkins of Worthing CID told The Argus he wants people who were in the park between 8.30pm and 10pm on Saturday night to contact him.
He said: “There is a ruptured gas main. We don’t know if that is due to or the cause of the fire.
“I am keen to hear from any people who were in the area at the time”
Officers are studying CCTV footage of the area.
The restaurant is set in Beach House Park, which is well known for its bowling greens and as the home of Bowls England.
Its former management claimed earlier this year to have invested a “six-figure sum” in the business.
In the last two months it is understood to have been taken over by new management.
Anyone with information is asked to call Sussex Police on 0845 6070999 or Crimestoppers anonymously on 0800 555111.