A huge crane (600-foot; 182.8-meter) collapsed at a Houston chemical plant killing four people and injuring six. The fatal incident occurred Friday during a routine maintenance at the chemical plant according to a company official.

The contract workers at the LyondellBasell-run refinery were getting prepared for the routine maintenance when the huge crane suddenly collapsed. The wounded were taken to hospitals near the plant. The four contract workers who were killed were employees of the crane's owner Deep South Crane & Rigging of Baton Rouge, Louisiana,

LyondellBasell official Jim Roecker described the incident as “a traumatic experience for all of us." Considering the fact that several similar accidents occurred over the past couple of months, the situation will most certainly heighten safety fears. Since March, two cranes collapsed in separate incidents in New York City killing nine people. There have also been crane accidents in Miami and Las Vegas.

The crane which collapsed at the Texas refinery was able to lift hundreds of tones. It had been delivered in pieces and assembled on site about one month ago, said Roecker, LyondellBasell's vice-president for refining.

The massive crane at the Houston plant collapsed at about 1400 (1900 GMT) on Friday. The Deep South Crane and Rigging-operated crane was not scheduled to work Friday. However, the structure’s engine was still running after it hit the ground, Roecker said.

The six people injured in the collapse were taken to the nearest hospitals. Two of them are reportedly in critical condition and the other four are with trauma-related wounds. About 1,500 contract workers are employed at the Houston plant.

"It's going to be quite some time before we know exactly what happened that caused the failure of this large piece of equipment," Roecker said.

Deep South, the firm which owns the crane said it is much too early to jump to conclusion on what caused the accident but it will initiate an investigation “to find out the root cause, correct it and ensure that this type of tragedy does not occur again".

The production of the 270,000 barrel per day (bpd) plant was not affected by the incident, said LysondellBasell Houston refinery spokesman David Roznowski during a news conference.