JACKSON (AP) — A gas pipeline exploded in rural Smith County in south Mississippi Wednesday, killing one person and leaving three others critically injured, officials say.

The explosion was reported around 4 p.m. on County Road 99 just south of Sylvarena, said Mississippi Emergency Management Agency spokesman Jeff Rent. The blast occurred on part of the Midcontinent Express pipeline belonging to Kinder Morgan.

‘‘There was a pressure test that was being conducted by a third party contractor on the Midcontinent Express pipeline when they had a failure,’’ said Joe Hollier, a spokesman for Kinder Morgan Inc. said. ‘‘It’s tragic that there was a loss of life. It’s never a good day when an accident like this occurs.’’

Hollier said the contractors conducting the tests were Beckville, Texas-based Grand Bluff Construction Co. and Priority Energy.

Rent said a fire in the area had been put out and there was no evacuation. He said he did not know how many workers were at the scene when the explosion happened.

A phone message left with a spokesman for Grand Bluff Construction was not immediately returned Wednesday evening.

Three medical helicopters lifted the critically injured from the scene, Jim Pollard, a spokesman for AMR ambulance service told The Clarion-Ledger newspaper in Jackson. All three were taken to the University of Mississippi Medical Center in Jackson.

Two had life-threatening injuries and the third was in stable condition, Pollard said. Officials have not disclosed their identities or the nature of their injuries.

Houston-based Kinder Morgan owns or operates more than 35,000 miles of pipelines and 170 terminals in North America.