SHIPROCK — Traffic piled up on U.S. Highway 491 in Naschitti on Thursday morning after a semitrailer carrying hazardous materials exploded near mile post 43.

The Navajo Nation Department of Emergency Management asked residents living within a two-mile radius of the crash site to evacuate beginning at about 11 a.m. The order was lifted by 2 p.m.

Rose Whitehair, director of the tribe's emergency management department, said a semitrailer exploded on the highway at about 6:40 a.m. Thursday. The department said in a press release that the hazardous material the truck was carrying has not been identified.

"We don't know what type of chemicals it may be," Whitehair said. "We don't know what particles are in the air."

Members of the San Juan County Hazardous Materials team helped extinguish the fire. New Mexico State Police, tribal law enforcement officials and staff with the Navajo Department of Transportation and the New Mexico Department of Transportation responded to the scene.

The Newcomb and Tohatchi chapters provided shelter for residents who live in the effected area. Residents were advised to stay away from the smoke and to close and lock the doors and windows of homes and vehicles while the fire burned.

Officials with New Mexico State Police could not be reached for comment. The condition of the semitrailer's driver is not known.

Southbound traffic on U.S. Highway 491 was diverted most the morning toward Navajo Route 5 and N.M. Highway 371.

No detour was available for northbound traffic in the morning. Traffic moved through the area using the southbound lane by early afternoon, but the northbound lane remained closed so that road crews could remove debris.

The cause of the explosion is under investigation.

Individuals are advised to seek medical assistance if they develop difficulty breathing, irritation to the eyes, skin, throat or respiratory tract, changes in skin color, headaches or blurred vision, dizziness or lack of coordination.

Reporter Steve Garrison contributed to this story.

Noel Lyn Smith covers the Navajo Nation for The Daily Times. She can be reached at 505-564-4636.