LOS ANGELES (CNS) - An investigation was underway today into a fire that heavily damaged an 11th-story apartment in a Brentwood high-rise, injuring at least 10 people, including three firefighters and a 2-year-old girl who was in critical condition after she was found on the 23rd floor of a smoke-filled stairwell.

Firefighters were sent to the 25-story Barrington Plaza complex in the 11700 block of Wilshire Boulevard, near Barrington Avenue, about 11:45 a.m. Friday on a report of smoke showing from the 11th floor, according to Brian Humphrey of the Los Angeles Fire Department.

At the height of the blaze, a plume of black smoke could be seen emanating from the structure, with flames shooting from west-facing windows.

Within about 45 minutes, the flames had been largely extinguished and the fire was declared out in an hour and 11 minutes. Despite what appeared to be two distinct plumes of smoke coming from the building, fire officials said the blaze was contained to a single two-bedroom apartment.

Two people were initially taken to a hospital for treatment of smoke exposure, Humphrey said.

However, as fire crews continued to search the building, paramedics found five other residents suffering from minor to moderate respiratory distress, Humphrey said.

Two of those injured residents declined to be taken to a hospital for treatment, Humphrey said. Among those who were taken to a hospital was a critically injured 2-year-old girl who was found with a man in a 23rd-floor stairwell.

Both were initially taken to the roof of the building for treatment, but then taken to the ground floor. According to reports from the scene, the girl was breathing when she was taken to a UCLA hospital.

``Firefighters did have to perform CPR on the girl and she is now with her doctors at a hospital,'' fire department Capt. Jaime Moore said.

Officials at Ronald Reagan UCLA Medical Center said three people were taken to that hospital, where one was treated and released and two others remained in critical condition.

Three firefighters also sustained burns and were taken to the Grossman Burn Center for evaluation of non-life-threatening injuries.

``Two of the firefighters have leg burns and the other has a burn to his ear,'' according to Humphrey. Those firefighters were released from the burn center Friday night, Humphrey said.

A dog was killed in the fire, Humphrey added.

Moore said that because of the aggressive tactics used by firefighters there was a great deal of water in the burned apartment unit and some of that water seeped into the floors below.

An estimated 100 to 150 residents from 51 units deemed uninhabitable have been displaced, Humphrey said, adding they had either secured their own alternate housing or were being assisted by the American Red Cross.

The cause of the fire remained under investigation by fire department units, including the arson unit. A damage estimate was not available.

The 240-unit building was built in 1961 and was not equipped with a sprinkler system because it was grandfathered in and was not required to have one, according to the LAFD.