By Amanda Orr and Andrea Lorenz

HOUSTON (Reuters) - Four firefighters died and five others were injured on Friday when a roof collapsed during a blaze at a hotel and restaurant in southwest Houston, fire department and city officials said.

Fire Chief Terry Garrison told a news conference that firefighters were searching for people who may have been trapped inside when the roof gave way. "They were in the highest amount of risk possible because we thought we had some civilians in the structure," he said.

"Unfortunately, the building had much more fire in it than we originally thought. The structure collapsed, and our members, while trying to save lives, were trapped."

At least one of the firefighters was in critical condition at a local hospital, officials said.

Texans are still reeling from the loss of first responders, including firefighters and paramedics, when a fertilizer plant in West exploded on April 17.

Garrison said the cause of the fire at the Bhojan Restaurant and Southwest Inn was under investigation. Firefighters called in just after 12 p.m. CDT (1300 ET) had the blaze under control by mid-afternoon.

Afterwards, some firefighters gathered at the back of a fire station about a half mile from the scene while others kept watch at the hospital.

"Houston firefighters mourn the loss of our three brothers and our sister and will forever honor their sacrifices," Jeff Caynon, president of the Houston Professional Fire Fighters Association, said in a statement. The union said it was the worst loss of firefighters in the history of that department.

Houston Mayor Annise Parker said, "There is nothing we can do that will heal the hurt that we all feel today," and added that the city would honor those who died.

Officials did not release the names of the firefighters who lost their lives.

(Reporting by Amanda Orr and Andrea Lorenz in Houston; Writing by David Bailey; Editing by Scott Malone, David Gregorio, Lisa Shumaker, Toni Reinhold)