No one was injured when a fire broke out late Sunday night at a Butler duplex, authorities said.

A couple in the upstairs apartment was home at the time, while the first-floor tenant was away.

The fire at 209 Third St. apparently started shortly before 11:50 p.m. on or around the deck in back of the second-floor apartment and spread inside, according to Capt. Kevin McAfee of the Butler Fire Department.

City police were first on scene. When it was not immediately known if anyone was in the downstairs apartment, police broke out a window to check.

Firefighters immediately began an exterior attack on the upstairs apartment, and soon a second crew moved inside.

The interior fire was contained to the kitchen of the second-floor apartment.

McAfee noted the door from the apartment to the deck was open, which may have allowed the fire to travel inside.

The deck, which had a roof over it, was destroyed, fire officials said.

The inside primarily sustained minor fire damage. The first-floor apartment had smoke and water damage.

The first-floor tenant arrived home after the fire started. A pet cat was found safe inside.

The cause of the fire is under investigation, McAfee said, but added the blaze did not appear to be suspicious. A damage estimate was not immediately available.

Authorities said the Red Cross was notified and is assisting the tenants, including Robert and Heather Potts who live upstairs, and the downstairs tenant, Michael Ross.

Barry Woolner owns the house. It was not known if he had insurance, or if the tenants had renter's insurance.

The Butler Township Volunteer Fire District and Butler VA Fire Department assisted city firefighters, who were back at their station around 1:30 a.m. Monday.