Clayton, N.C. — Johnston County emergency officials began a voluntary evacuation of homes within three miles of a fire that is pumping smoke and fumes from burning tree stumps.

Three people spent Tuesday night in a shelter set up at Clayton High School's new gym for those wanting to evacuate their homes.

Johnston County communications centers workers said they initiated reverse 911calls about midnight after air monitoring showed heightened levels of carbon monoxide in the air.

The voluntary evacuation was aimed particularly at people with respiratory problems, who might be more affected. Earlier, people with respiratory problems had been told they should limit their outside activities.

Officials advised people who wanted to stay at home to keep windows and doors shut and to turn off their air-conditioning and heating systems to prevent them for drawing outdoor air into houses.

The fire was expected to cause problems periodically for a couple of days, county officials said.

The fire broke out at the stump dump off Loop Road. The state Department of Environment and Natural Resources required Stump Dump Inc. to cover its yard waste with dirt, which representatives say is standard practice. Something caused the fire to combust spontaneously, however.

According to officials, the fire started under the dirt before spreading and erupting into a huge cloud of smoke. The fire is expected to burn for several days, causing heavy smoke in the early morning and late afternoon hours.

Motorists were urged to be cautious on the roads because heavy smoke is a concern for that area. The state Division of Air Quality is investigating the incident.