Six utility workers were injured in an electrical explosion at a dam in central Washington state Thursday.

Grant Public Utility District spokesman Thomas Stredwick told the Associated Press the structure of the Priest Rapids Dam is stable and no residents are at risk.

Multiple agencies responded to the incident including the Hanford Fire Department. The Grant County Sheriff's Office told the Tri-City Herald the incident occurred at approximately 4:15 p.m. local time.

The dam is located on the Columbia River near Mattawa, Wash., about 60 miles east of Yakima.

Three of the six injured arrived at Harborview Medical Center in Seattle Thursday night for burn treatment, according to spokeswoman Susan Gregg. Two men, both in their 40s, were in critical condition and expected to be placed in an intensive care unit. A 58-year-old man was in satisfactory condition, she said.

Hospital officials were expecting another man involved in the explosion to arrive later Thursday night.

Stredwick said he didn't know where the other two injured were taken for medical treatment.

There was no immediate word on what caused the blast but Grant County Sheriff's Office spokesman Kyle Foreman said they've found no connection to terrorism or criminal activity.

Some residents in the rural, largely agricultural area were without electrical power Thursday evening and cellphone service related to the blast, Stredwick said. He said 911 call service may also have been out briefly.

The Priest Rapids Dam was built in the 1950s and is one of two operated by the Grant Public Utility District along the Columbia River to provide power to residents.

The Associated Press contributed to this report.