LITTLETON, Colo. — A fire in a suburban Denver apartment complex for seniors created smoke so thick it trapped some people in their homes early Saturday, injuring more than a dozen people, including three seriously, authorities said.

Police officers and firefighters guided residents out through smoky hallways at the Littleton community for people age 55 and older, South Metro Fire Rescue spokesman Eric Hurst said. Residents of upper floors waited for an all-clear on their balconies, away from the heavy smoke.

The fire reported early in the morning was contained to a first-floor unit inside the six-story building.

At least 13 people were taken to hospitals, including three in serious condition, Hurst said. Ten others were in stable condition.

Authorities told Denver news station KCNC-TV that at least one person was hurt jumping from a second-floor balcony. They said others suffered smoke inhalation.

About 50 residents spent the morning at a nearby church, waiting for news on when they could return home. It was not clear how many people live in the building.

Karlene Austgen, a 67-year-old who has lived in a second-floor unit for four years, told The Denver Post that the smoke created by the fire made it difficult to see. She brought her 8-year-old cat named Zuzu with her to the shelter run by the Red Cross.

"I couldn't see a thing because of all the smoke," Austgen said. "Thank God I had my oxygen, or I wouldn't have made it."

Officials have not determined what caused the fire yet.