A gunman walked into a Fort Worth church during a prayer rally for teenagers tonight and opened fire, killing seven people and wounding several others before turning his weapon on himself, authorities said.

The unidentified assailant, who appeared to be in his thirties, entered Wedgwood Baptist Church shortly after 7 p.m. and fired numerous shots as more than 150 young people and others in the sanctuary screamed and dived for cover, witnesses and police said. Police said seven people died in the church, including the gunman, and one later died at a hospital.

At least three of the dead were teenagers, authorities said. Seven people were hospitalized with gunshot wounds, and at least two were in critical condition.

Witnesses told reporters at the scene that the assailant reloaded his weapon at least once.

There are "cartridges, shrapnel and empty cart boxes and blood splattered all over the wall," said Fort Worth police spokesman David Ellis.

A fire department spokesman, Steven Kerr, said some witnesses also reported hearing an explosion, and that bomb technicians were searching the building for explosive devices. "There have been reports [that] possibly a pipe bomb had gone off during the shooting," he said. Authorities reported finding potential bomb fragments.

"He hits the door real hard to make his presence known and he just immediately started firing," the Associated Press quoted Dax Hughes, the church's college minister, as saying.

"I saw him keep shooting and reloading. . . . He'd empty and reload," one young survivor told reporters outside the red-brick church in the southwest section of Fort Worth.

"I just saw him point and shoot," another witness, Christy Martin, 17, told reporters. She said the gunman appeared "very calm and looked normal and was smoking a cigarette."

Daniel Cox told Fox News: "A friend of mine and I were in back. We heard some tat-tat-tat, really loud. . . ." They peeked around the door and saw smoke. "We ducked back in, and I noticed some glass shatter and I just ran." Cox said he had not seen his friend since they were in the church together.

Fort Worth Police Chief Ralph Mendoza said the shooter was a white man armed with a semiautomatic weapon but that he had not been immediately identified. The assailant and his victims were still in the church tonight as relatives, friends and others stood outside, crying and bomb technicians searched the church for explosives.

After the bomb squad found several "secondary devices" believed to be explosives, investigators from the federal Bureau of Alcohol, Tobacco and Firearms evacuated a two-block area around the church while the search for explosives continued.

Chris Applegate, 12, told a local television station he was in choir practice when the gunman burst into the room.

"We were singing a song and then in the middle of the song this guy opened the door and fired one shot," he said. "He just kept telling us to stay still.

"We all just jumped under the benches and he fired about 10 more shots. . . . Somebody said, `Run! Run!' " and we all started running."

The prayer rally attracted teenagers not only from Wedgwood's congregation but from other churches, officials said. Kerr said the assailant, described as wearing black, apparently did not speak before opening fire.

"At this moment we are not aware of any conversations transpiring with any of the people inside the church or with any of the victims," Kerr said. As for a motive, he said, "It's really a mystery. . . . We don't know if he's affiliated with the church or whether he knows anybody at the church. It's really a sad situation."

"This is a terrible tragedy made worse by the fact that it took place in a house of hope and love," Texas Gov. George W. Bush said in a statement.

Rachel Shipp, 18, shared that sentiment. One of her friends had been killed, another seriously wounded and a third could not be found.

"I'm frantic, I'm in shock," the Dallas Morning News quoted her as saying. "You would think a church would be the safest place for children, especially in Wedgwood. This is where you praise God."

Special correspondent Khiota Therrien contributed to this report from Washington.