NEWPORT, Wash. - An explosion ripped through the Zodiac Aerospace plant in Newport Tuesday night, sending five employees to the hospital and forcing area residents to evacuate.

The blast occurred shortly before 9 p.m. and happened in the back portion of the building. The explosion caused one floor to collapse on top of another. Windows were shattered and doors were blown off their hinges.

Residents on the scene said they heard the blast from as far as a mile away.

Of the five people injured, three were released from Newport Hospital, according to Pend Oreille County Undersheriff Grant Sirevog. He added that one is in stable condition and the condition of the final person is unknown.

The cause of the explosion is under investigation.

"Although it's still unclear exactly what happened, it could have been a flammable vapor explosion," Assistant Spokane Fire Chief Brian Schaeffer said.

Chemicals including acetone and alcohol were believed to be on site and although a hazardous materials team from Spokane was dispatched, it was recalled before arriving.

The evacuation order was lifted by 3 a.m. Wednesday.

The Zodiac Aerospace plant employs 85 and city officials feel the loss will have a significant impact on the local business economy.

Newport Administrator and Building Official Ray King estimated the explosion caused $1 million in damages to the plant.

"From what I understand with the damage to the building and its contents, the business is a total loss. It was pretty horrific," Newport Mayor Shirley Sands said. "You have injury to employees and loss of employment brought to the city of Newport. There are not a lot of jobs out there and now it's even harder on those who had their lives changed in an instant last night."

According to the Wall Street Journal, Zodiac is one of the world's largest suppliers of aircraft interiors to airplane manufacturers like Boeing and Airbus. The Newport plant is part of Zodiac's "cabin and structures" division and makes components for cabin interiors.

In a statement released on Wednesday the company said, "Our first thoughts go to our five colleagues who have been injured in the accident and to all the personnel and families of our employees in Newport."

The release went on to state, "the cause of the explosion is not known and will be investigated both internally as well as with local and government officials. Zodiac Aerospace will fully support the inquiry. The assessment of the consequences of this explosion is underway."