Skylar Meade, 31, a documented member of the Aryan Knights white supremacist gang serving time for aggravated battery, was last seen fleeing Saint Alphonsus Regional Medical Center in a car with his accomplice, Boise Police Chief Ron Winegar said.

He had been housed under administrative segregation, a form of solitary confinement for inmates deemed especially dangerous, at the Idaho Maximum Security Institution near Kuna, Idaho, according to state Corrections Department chief Josh Tewalt.

Meade was taken to the hospital on Tuesday night for treatment of what Tewalt called "self-injurious behavior" that prison staff deemed serious enough to warrant emergency medical care.

At about 2:15 a.m. local time on Wednesday, as three corrections officers were preparing to transfer him back to prison, an individual waiting at the hospital's emergency department opened fire on the guards, wounding two of them.

One was listed in critical but stable condition, while the other was hospitalized with serious but non-life-threatening injuries.

A third correctional staffer was slightly injured in the ensuing pandemonium by gunfire from a Boise police officer called to the scene, authorities said.

By then, Meade and his accomplice had already made their getaway, Winegar told reporters at a news briefing hours later.

The police chief said law enforcement agencies throughout the state and surrounding region were searching for the two fugitives and anyone else who may have been involved in what he said was a planned, coordinated attack.

Tewalt called the breakout "unprecedented" in nature.

Authorities issued a bulletin with photos of the getaway vehicle, a gray four-door sedan, and pictures of Meade, whose face is tattooed with the numerals 1 and 11, which Winegar said stand for letters A and K, the abbreviation of Aryan Knights.

Meade has been incarcerated since 2016 and was serving a prison sentence that was scheduled to run until October 2036, becoming eligible for parole in 2026.

The police chief said authorities would welcome any tips that might lead to Meade's arrest while warning members of the public to keep their distance from both Meade and his accomplice.

"They are dangerous, they are armed and they have shown a propensity for violence," he said.

(Reporting by Steve Gorman in Los Angeles; Editing by Chris Reese)

By Steve Gorman