The first two firefighters headed into the burning warehouse to search for homeless people who might be inside. Minutes later, a voice crackled over the radio: "Mayday, Mayday, we're running out of air."

Four other firefighters disappeared into the smoke in an attempt to rescue their colleagues.

None returned.

The six Worcester firefighters are believed to have perished in the five-story conflagration that continued to burn this morning.

"It's three weeks before Christmas. There's roughly 15 kids out there without fathers," said District Fire Chief Michael McNamee.

Investigators said the cause of the fire was not immediately known. But Worcester Deputy Fire Chief Gerard Dio called it suspicious, saying firefighters initially were fighting two fires that appeared to have started separately.

Witnesses told firefighters that homeless people often built fires in the windowless rooms of the old abandoned cold storage warehouse to keep warm.

For the firefighters who entered it Friday night, the 80-year-old building became a confusing maze of dark, smoky rooms with no windows, which impeded their ability to find their way and trapped the heat inside. Cork insulation added to the smoke.

As the warehouse continued to smolder today, family and friends of the six were escorted to the warehouse. As firefighters continued to douse the hulking frame with water, the families dropped off flowers before being bused to a nearby church.

Worcester Fire Chief Dennis Budd said firefighters did not find any sign that homeless people had been trapped in the building, although investigators were checking with homeless shelters to see if anyone had been reported missing.

CAPTION: Firefighters in Worcester, Mass., battle a blaze Friday night in an old warehouse reportedly used by homeless.