Discarded cigarettes have been determined to have caused a fire to break out on the second floor of a four-unit house on Sussex Avenue Wednesday afternoon.

The fire, which began at about 2:30 p.m., began in the rear of 30 Sussex Ave., according to Morristown Acting Fire Chief Robert Flanagan. It was under control within 30 minutes and completely extinguished by 3:40 p.m., he said.

Only three residents of the property, an old house converted into multiple apartments, were at home at the time of the fire and were evacuated, he said. One firefighter at the scene was treated at Morristown Medical Center for heat exhaustion and was later reported to be in good condition, Flanagan said.

While the fire affected two second-floor units, the entire property has been deemed uninhabitable due to smoke and water damage throughout the whole house, Flanagan said.

Sussex Avenue was closed up to Mills Street while firefighters, which included the RIT Team from Cedar Knolls, fought the blaze. It was expected to reopen shortly before 5 p.m.