By Eric M. Johnson

Nov 23 (Reuters) - Five workers were injured after a fire and tank explosion at an Encana Corp natural gas field in western Wyoming on Friday, officials said.

Police said they received multiple calls about a blast at about 10:18 a.m. local time at Encana's Antelope 91-29H facility in the Jonah Field near Pinedale, about 230 miles (370 km) west of Casper in the western U.S. state.

One of the injured workers was airlifted to hospital in critical condition and the others were taken by ambulance to a local clinic and hospital, said Bridget Ford, a spokeswoman for Encana Oil & Gas (USA) Inc, without giving further details.

"We know that some welding work was being conducted on the condensate tanks on location, however the exact reason for the explosion is not known at this time," she said.

Firefighters contained the blaze, which burned out by 1 p.m., Ford added.

A drilling rig is operating near the facility where the incident occurred but it was not affected, she said, adding there was no apparent environmental impact.

"Our thoughts are with our friends and co-workers that were hurt today, and their families, Ford said.

Encana and the contracting company are working with the Occupational Safety and Health Administration, which is investigating the incident, she added.