BOULDER, Colo. -- A chemical reaction and subsequent fire prompted the evacuation of the Lexmark plant on North 63rd Street in Boulder Thursday morning and forced people working in the IBM buildings around it to move to the center of the campus.

According to investigators, two epoxies were being mixed at the Lexmark plant when a fire started just after 8 a.m. The fire caused a large smoke plume containing irritants.

Witnesses at first said that the "white chemical cloud" was seen first over the Lexmark building and then appeared to drift over the IBM buildings at 63rd Street and Monarch Road.

More than 150 employees at Lexmark were evacuated while employees in the other buildings nearby were told to stay indoors until further notice.

Boulder County authorities also implemented a reverse-911 call warning people within a two-mile radius of the chemical fire. Residents were told to take "shelter-in-place" and asked to stay in their homes and shut all windows and doors.

Firefighters were called at 8:07 a.m. when seven people at Lexmark started complaining of respiratory problems, said Boulder Fire spokesman Justin Dombrowski.

Six people have been transported to Boulder Hospital where they were treated and released.

Hazmat workers decontaminated approximately 100 Lexmark employees using soap and water. Crews also decontaminated the site.

Authorities do not know when the cleanup will be completed.

Authorities still don't know exactly what chemicals were used. The chemicals, said to be a liquid plastic, were part of a floor retiling or coating project that was not related to Lexmark's manufacturing of printers.

"We were told it is an irritant. So, some of the people on the scene, as expected, are experiencing various sensations to the nose and to the eyes. And they could also be experiencing respiratory difficulty as a result of this irritant," said Boulder police spokeswoman Julie Brooks.

Brooks said authorities will set up a recorded message phone line so that people who are concerned, and who may experience these symptoms later, will know what to do.

The Regional Transportation District was in the area in case its buses were needed to help get people out of the vicinity, which is primarily an industrial area. People who were evacuated gathered near the Boulder Reservoir to get on the bus.

During the cleanup, the Diagonal Highway between 63rd and Niwot was shut down and 63rd was closed between the Diagonal Highway and Monarch. The Diagonal Highway was reopened just before 11 a.m.

The nearby Sheperd Valley Waldorf School was also evacuated and was closed for the rest of the day.

Lexmark International Inc. manufactures computer printers and printer supplies. The building was closed for the rest of the day.