Washington, Mar 4 (IANS): Five people are in critical condition after an explosion in an apartment complex in the US state of Maryland's Montgomery County, according to authorites.

One section of the four-storey apartment complex, just several kilometres outside of Washington, D.C., was levelled into a pile of blackened, smoldering wreckage, reports Xinhua news agency.

Firefighters rushed to the scene at about 10.30 a.m. on Thursday, and they were able to help some residents escape before the building was consumed by fire and collapsed, according to Montgomery County Fire Chief Scott Goldstein.

Goldstein also told reporters about 125 to 150 firefighters had responded to the scene, saying that "it's too early to speculate" on a cause.

Seven or eight people have less serious injuries, and some of them were transported to the hospital, Montgomery County Fire and Rescue spokesman Pete Piringer said.

"This is obviously a really tragic event," Montgomery County Executive Marc Elrich said later, adding that county officials would step in to offer shelter and other aid to residents of the apartments.

Maryland Governor Larry Hogan said that state officials were in contact with Montgomery County authorities to offer assistance.