Boston ? Fire broke out in a restaurant ceiling and smoldered above diners and employees for an hour or more before erupting, killing two firefighters and injuring 10 who became disoriented, officials said Thursday.

A paramedic was also injured, but no employees or customers were harmed in Wednesday night’s four-alarm fire at the one-story Tai Ho restaurant. The blaze also damaged a block of businesses.

When workers first saw the fire, they quickly evacuated the restaurant and called 911.

But while the fire smoldered unnoticed in a grease-filled crawl space above the drop ceiling, toxic and flammable gases had collected, Fire Chief Kevin MacCurtain said, and what looked at first like a routine fire quickly turned deadly.

“When they started to extinguish the fire, something unexpected happened,” he said. “Very quickly and very suddenly the entire ceiling was blown down under force, and a volume of fire was pushed down that had accumulated in that crawl space.”

The firefighters likely became disoriented and could not find their way out, he said.