A suspected explosive device discovered by fire investigators after they were called to a possible arson at a restaurant in Hove has been made safe.
Police cordoned off the area in Kingsway and evacuated nearby buildings after the package was found at 1120 GMT at Breakfast at Tiffany's.
Officers said a lit object that caused the suspected arson and the explosive device were thought to be connected.
A bomb disposal team was sent to carry out a controlled explosion.
The alarm was raised at 0015 GMT when a passer-by spotted flames as he drove past the restaurant.
The man helped the family living above the premises to safety, East Sussex Fire and Rescue Service said.
A total of 13 firefighters dealt with the initial incident and when fire investigators returned later in the morning to examine the scene in daylight, they discovered the device.
East Sussex Fire and Rescue Service crew manager John Coppard said: "If it wasn't for the fact the family had working smoke alarms, and that a passer-by stopped, it could have been quite a different story.
"The man had been driving to pick his girlfriend up from a function in the town.
"We praise his actions for stopping to help. Not many people would do that nowadays."
Det Insp John Wallace said the suspected arson had happened after a lit item was thrown through the glass window of the restaurant's front door. The suspected explosive device was later found inside the restaurant.
He said: "We now believe that the two objects were in fact connected. It appears the first element was made up of a large quantity of flammable materials, coupled with the second one which was a potential explosive device.
"However further detailed forensic analysis will be necessary in order to confirm this beyond doubt."
He said police were keeping an open mind about motives but added: "We do not believe this is a random attack on the premises."
And he said: "Fortunately the flames from the first part were put out quickly, before the suspected explosives could ignite. Otherwise the damage, and danger to the lives of those upstairs or passing by, could have been considerable."