A house fire that killed six children and three adults in Memphis was caused by an electrical malfunction in an air conditioning unit's power cord in the living room, authorities said.

The Memphis Fire Department released the cause of Monday morning's deadly fire as relatives and friends mourned their loved ones by hugging, crying and holding hands in prayer outside the house in a working class neighborhood in south Memphis.

Meanwhile, a 10th victim of the fire, a child, is fighting for life at a hospital.

Firefighters initially spotted light smoke outside the single-story wood-and-brick home when they arrived at 1:23 a.m. but encountered heavy smoke inside, Memphis Fire Services Director Gina Sweat said. The fire was brought under control in 19 minutes.

Fire crews found three adults and four children dead in the home, the fire department said. Two other children died after being taken in extremely critical condition to a children's hospital, Sweat said.

One other child remains hospitalized, said Sweat, who called it the deadliest fire in Memphis since the 1920s. More recently, seven people died in a fire here in 2008, fire department spokesman Wayne Cooke said.

Investigators determined that the house did have a working smoke alarm, the fire department said. The inside of the home was charred, but the house didn't burn down and fire officials said only part of the house was affected by the fire.

The wooden-frame home has a brick facade and bars on some of its windows and doors. It wasn't immediately clear if those inside had tried to escape through the windows, Sweat said. Window bars present a danger for people trying to escape a house fire, though many window bars have releases that can open them from the inside, she said.

"They could have been simply overcome by smoke and never had an opportunity to escape," she said.

Memphis Mayor Jim Strickland asked for prayers for family members of the dead, who weren't identified Monday. Some of the victims had signs of smoke inhalation, while others had burns, according to authorities.

"It's a very sad day," Strickland said. "We are all in mourning."

Sweat went to the site and spoke with firefighters shocked by the loss of life.

"You could feel the heavy in their hearts, and you could see the pain in their eyes," she said.

Hours after the fire, a woman knelt on the ground outside the home and wept. Other people hugged each other and prayed together along the street. A red motorized children's toy truck and a red bicycle with no wheels sat outside of the home.

Felecia Wallace, 34, said she has known the family since she was in elementary school. She said she once needed bus fare to get to work and someone who lived in the house just gave it to her.

"This is a loving family," Wallace said. "If you needed anything, you could come right here. If you were hungry, you could come right here. If you needed a place to sleep, you could come right here."

A fund to help the family has been established at Regions Bank, under the name Toots Family Funds.