WEST, US - The seat, or center of an explosion that blew off a fertilizer plant and almost razed the US town of West had been located, a US Official said Sunday.

Assistant Texas fire marshal Kelly Kistner told a press conference here that the locationing of the center of the explosion is important to the investigation of the the blast. But he said the cause of the fire and blast remained unknown.

The explosion left a large crater in the middle of the plant, said Kistner, but declined to elaborate on the dimension of the crater or give other details.

Kistner confirmed that all fires at the explosion scene have been extinguished and the remaining tankers are not a danger.

Authorities of West on Saturday imposed a curfew and allowed some residents to return to their homes, almost two days after the explosion.

Steve Vanek, mayor pro tem of West, said Sunday that the re- entry of the residents went smoothly. The process "is going well and orderly," ?he said.

There will be three phases for the residents' returning, but the timeline for phase-2 and phase-3 re-entry has not decided yet, he said.

The powerful blast occurred around 7:50 p.m. Local time Wednesday at the fertilizer plant in West, a small town some 320 km north of Houston, Texas, killing at least 14 people and injuring about 200 others. Another 60 remained accounted for in the blast, according to local officials.