ALLENTOWN, Pa. - February 10, 2011 (WPVI) -- Police and firefighters are searching for six people who are unaccounted for, following a massive gas explosion in Allentown that spawned fires, downed power lines and prompted the evacuation of two city blocks.

Officials are describing the search as a recovery effort.

Crews for UGI, the gas company that services the Allentown area, have managed to shut off the gas. Officials say that removes the risk of a second explosion.

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Firefighters continue to pour water on buildings that are still burning.

Officials say between 500 and 750 people, including those living at a senior citizens home, had to be evacuated.

The blast blew out many of the windows of that senior citizen home.

The explosion took place at about 10:50 on Wednesday night at North 13th and West Allen streets.

Eight homes at the blast site have been destroyed, a total of about 30 homes have been damaged.

When firefighters arrived they saw flames shooting out of the street's manholes.

Gas company crews initially had a very difficult time locating the gas line break and shutting off the gas.

The explosion sprayed debris for blocks.

Eight residents were taken to the hospital with minor injuries, and a firefighter twisted an ankle.

Now that the gas has been shut off, some residents have been allowed to return to their homes, including all of the residents of a large apartment complex in the area.

But those who lived closest to the blast site may not be able to return for days.

Many of the evacuees have been taken to the Allentown Fair Grounds or a nearby hotel.