(CNN) -- A bomb exploded at a Woodburn, Oregon, bank branch early Friday evening, killing a police officer and injuring the town's police chief and a state bomb technician, Oregon State Police said.

A police officer was killed Friday after a bomb exploded inside the West Coast Bank in Woodburn, Oregon.

Woodburn Police Chief Scott Russell was listed in critical condition at Oregon Health and Science University Hospital, according to hospital spokeswoman Christine Decker.

The name of the slain police officer has not yet been released. There was no immediate word on the bomb tech's identity or condition.

The three were investigating a suspicious device at a West Coast Bank branch when the bomb went off, police said. Police had brought the device inside after it was discovered outside, bank president Bob Sznewajs told CNN.

Sznewajs said that two bank employees who were in another part of the bank when the bomb exploded suffered very minor injuries, one who may have been hit by some flying debris and another who was "bothered by the sound."

"I know that all of our employees are fine," Sznewajs said, adding that none of his employees had been allowed back into the front portion of the building, where the bomb exploded, "so we don't know what it's like in there."

"I heard a loud kaboom," Robert Currie, who was across the street, told CNN affiliate KATU. "Well, I'm a Vietnam veteran and that was no gunshot -- that was definitely a bomb. So I come running outside to see what was going on and the interior lights of the bank are all out. And the next thing, it's just swarming with police cars, two fire trucks and three or four ambulances."

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Several emergency vehicles surrounded the building, according to news video from the scene, but the exterior of the building did not appear damaged.

Sznewajs said police were called to investigate a suspicious package Friday afternoon. Police gave the all clear, Sznewajs said, but a bank employee saw something in a bush outside the bank, and police were called back.

Sznewajs said he was not at the bank at the time of the incident, but he said his employees told him authorities "scanned it outside, then brought it in."

His employees had left the front of the building by that point, Sznewajs said, and it was not clear why the device was taken into the building.

Sznewajs said there were "four or five" employees in the bank when the incident began and approximately the same number of customers. None were in the front of the bank when the explosion took place.

Earlier Friday, police investigated a bomb threat called into a nearby Wells Fargo Bank branch but found nothing, Wells Fargo spokesman Tom Unger said. The call came in before 10:30 a.m., Unger said, and the branch closed at 2 p.m.

The Wells branch and the West Coast branch are less than 150 feet apart.

Woodburn is in the Willamette Valley about 30 miles south of Portland.

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