Workers were rushing to remove the debris and investigate the cause because a major winter storm was forecast to hit the area Wednesday evening, James said.
"We have a major storm coming in this evening," James said. "We're going to work diligently to get in (to the blast site) to get underneath that weather."
Berardi said firefighters were called about 5:15 p.m. with a report that a construction worker had hit a gas line near the restaurant. Firefighters conferred with MGE workers and left the scene, and the explosion occurred about 45 minutes later. He said the cause of the gas leak and fire is still unknown.
"Once we confirm the victim is or isn't inside the building, that part of the investigation will continue," Berardi said.
JJ's had managed — until Tuesday night — to survive in the shadow a large construction project that has been under way across the narrow, one-way street for seven years. The work had complicated access to the street-corner restaurant, and a server needed hospital treatment in 2006 after she was struck by a rock sent flying by blasting for excavation of the construction site.
It was not known whether the contractor said by MGE to have been doing underground work was connected to the construction project.
Dr. John Verstraete, who works at Plaza Physicians Group next door to JJ's, told The Kansas City Star that several employees of the office smelled gas for several hours Tuesday afternoon. The smell grew stronger through the day, and a gas company employee entered the medical office just before 6 p.m. recommending that it be evacuated, he said.
The blast shattered windows in some businesses at a small strip mall nearby, and residents of some neighboring apartments reported minor interior damage. One side of a brick apartment building that shares the block with JJ's appeared to have been scorched.