Four Houston firefighters have died and another five people were injured in a massive hotel fire on the city's southwest side Friday afternoon, city officials say.

At about noon, firefighters were called to the Southwest Inn on the 6800 block of Southwest Freeway after a fire broke out inside the inn's restaurant and quickly engulfed much of the hotel.

Three of the firefighters were killed at the scene, while the fourth died at a hospital, according to the office of Houston Mayor Annise Parker and the local medical examiner.

According to Jeff Canyon, president of the Houston Professional Fire Fighters Association, field reports indicate that the firefighters were caught in a roof collapse.

"I don't know if that was folks outside next to the structure or inside when it collapsed, but the collapse is going to be the cause," he said after visiting with firefighters at Memorial Hermann Hospital.

The firefighters have been identified as Capt. EMT Matthew Renaud, 35; Engineer Operator EMT Robert Bebee, 41; Firefighter EMT Robert Garner, 29; and Probationary Firefighter Anne Sullivan, 24, KPRC reported.

Five other firefighters were injured and are being treated at three Houston hospitals for chest pains or leg injuries. One is listed in critical condition, and the four others are stable.

"It's a very sad day for the Houston Fire Department and the city of Houston as a whole," said Janice Evans, a spokeswoman for Parker.

When a flag-draped body was removed from the smoldering remains around 4 p.m., some four hours after the blaze broke out, firefighters -- working in swirling winds, steamy humidity and temperatures exceeding 90 degrees -- paused and saluted. A procession of ambulances, under police motorcycle escort, left the scene about 90 minutes later and made a ceremonial drive past the fallen firefighters' station, by then draped in black.

"We will provide appropriate services to our fallen firefighters and full honors, but there is nothing we can do that will heal the hurt that we all feel today," Parker said. "I ask for every Houstonian to offer their prayers to the families of these fallen firefighters, and also to think about what the job of firefighter is and the dangers they face every day."

Flames could be seen shooting through the roof and sending plumes of smoke over the freeway, obstructing the vision of nearby drivers. Ahead of rush hour Friday afternoon, white smoke could still be seen rising from the shell of what remained of the hotel.

About 150 firefighters took two hours to put out the five-alarm fire, according to the Associated Press, though the fire was still smoldering several hours later.

The cause of the fire is not yet known.

So far this year at least 19 first responders have been killed in the line of duty in Texas. That number includes the 14 first responders killed in West, Dallas-Fire Rescue's Stanley Wilson, who was killed in an apartment building fire May 20, and the four Houston firefighters killed Friday.

The loss of life is believed the single worst in the history of the 116-year-old Houston Fire Department, Evans said.

The department had counted 64 firefighters lost since the city began paying firefighters in 1895. Twice previously, two firefighters were killed in a single fire, in 1953 and most recently in 2000. Three firefighters died in 1929 when a train slammed broadside into their engine.