HASTINGS, Neb. (AP) — A lightning strike at a Nebraska fertilizer plant set off a large fire that injured three truck drivers sleeping in the parking lot and destroyed the unoccupied factory, officials said Friday.

The fire was reported about 11:30 p.m. Thursday at the Cooperative Producers Inc. dry fertilizer plant in Hastings, about 160 miles (257 kilometers) west of Omaha. Crews worked most of the night and contained the fire just before 4 a.m. Friday.

The blaze forced authorities to close U.S. Highway 6 for several hours. A release from the Adams County Emergency Management office says railroad tracks just north of the plant also were closed for a time before being reopened.

The Nebraska Fire Marshal’s office said in a news release late Friday afternoon that an investigation showed the fire was sparked by a lightning strike.

Fire Chief Bob Hansen said no one was in the building when the fire happened. The injured semitrailer drivers were treated and released from a hospital, the Hastings Tribune reported. No firefighters were injured.

Hansen said the plant was already fully engulfed in flames when firefighters arrived. Three other departments from nearby towns were called in to help fight the huge blaze.

“We were utilizing every hydrant we could,” Hansen said.

Firefighters considered evacuating nearby mobile homes, but a shift in the wind blew heavy smoke away from them and made evacuation unnecessary. Hastings residents with health conditions that could be exasperated by smoke were urged to keep their windows closed and air conditioners off Friday.

“We’re waiting for the smoke to clear to use a drone to fly over and see pictures of the inside,” Hansen said.

The CPI plant opened last year with plans for storage capacity of 42,000 tons of product. The preliminary damage estimate for the building is $14 million. The damage to products inside the building is estimated at another $5 million, according to the fire marshal’s office.