The services began at about 9:30 a.m. at the Cathedral of Our Lady of Angels, 555 W. Temple St.. Services were preceded by a walking procession of mourners from the south lawn of Los Angeles City Hall to the cathedral.
During the procession, Allen's flag-draped casket was transported aboard a fire truck assigned to Fire Station 97, where he was stationed, and carried into the cathedral by pallbearers accompanied by bagpipers.
Chief Millage Peaks displayed Allen's badge to the mourners, and described his fallen colleague as a hero.
"The word 'hero' is too often used to describe the most routine and common behaviors ... but exceptional deeds, noble qualities, exceptional bravery, and special ability are what (define) an authentic hero, and firefighter Allen lacked for none of these qualities," Peaks said.
A colleague who spoke near the beginning of the service described Allen as quiet around the engine house, and very considerate of others. He was always the first to arrive for his shift.
An estimated 8,000 mourners were expected to be in attendance, about 250 of them dignitaries, including Gov. Jerry Brown, Los Angeles Fire Department Chief Millage Peaks, and Los Angeles Mayor Antonio Villaraigosa, said LAFD Capt. Tina Haro.
Haro said about 100 public safety agencies will be represented, and there will be three Honor Guards, and 200 pieces of emergency apparatus at the scene.
Following the funeral, a memorial reception will take place, beginning about noon, at the Frank Hotchkin Memorial Training facility in Elysian Park. Burial will be private.
Allen, 61, was a 36-year veteran of the LAFD, and about a year from retirement. He was injured when a ceiling collapsed on him and five other firefighters during a blaze that broke out late on the night of Feb. 16 in a mansion in the 1500 block of North Viewsite Drive. He died last Friday at Cedars-Sinai Medical Center.
This week, the site was declared a "crime scene" and LAPD Robbery Homicide Division detectives were conducting an investigation, along with personnel from the fire department and the city. The investigators reportedly were trying to determine if any building and safety codes were violated. Such codes are designed not only to protect the public, but also to protect first responders to the scenes of emergencies. It was unclear if any criminal charges could be filed.
Officials said earlier that the fire was thought to have been sparked by a faulty gas fireplace.
Allen was the first LAFD firefighter to be killed in the line of duty since March 2008. when Brent Lovrien was killed in an explosion near Los Angeles International Airport as he investigated an earlier blast that blew manhole covers into the air.
Allen's daughter gave birth on the day after he died to his first grandson. The 6 pound, 7 ounce boy was said to be healthy.
Allen is survived by his wife, Melanie; his daughter, Rebecca McPhee; his son-in-law, Brandon McPhee; his grandson; his mother, Alberta Holtze; his brother, Bruce Allen; and his sister, Deborah Abrams.