Updated

McKINNEY, Texas -- A man drove a pickup truck loaded with ammunition into a suburban Dallas police station's parking lot Tuesday, set the truck on fire and exchanged gunfire with police, officials said. The gunman was the only casualty and died at the scene.

McKinney Deputy Police Chief Scott Brewer said the man was shouting as the truck became engulfed in flames and the ammunition inside began exploding. The still-unidentified gunman then began shooting toward the police station and there was a "brief exchange of gunfire," Brewer said.

It wasn't immediately clear how the gunman died.

Brewer said police had no idea why the attack occurred or whether the man planned the attack alone.

"We believe there is just one shooter at this point in time," Brewer told reporters at McKinney City Hall. The police station sits amid a large cornfield near Collin College.

One building on campus was hit by bullets, but there were no injuries, said campus spokeswoman Lisa Vasquez. The college locked its campus down to students and staff for two hours after the shooting, and has blocked access to the public, Vasquez said. Patrol cars blocked street entrances to the McKinney police department building.

A police officer was seen late Tuesday morning poised with a shotgun near a pickup outside the Public Safety Building in McKinney, a suburb of about 127,000, about 30 miles north of Dallas.

Department of Public Safety spokesman Tom Vinger said Texas Rangers, highway patrol and DPS aircraft were on the scene or headed to the area. Vinger could provide no further details.

The Collin County Community College District sent an e-mail alert to college staff and students shortly after 9:30 a.m. Tuesday warning that shots had been fired and that the central campus in McKinney was closed.

The e-mail said: "Shots fired. Campus on lockdown. Cops on the scene. Details to follow."