A woman apparently upset about the firing of a friend took three people hostage at gunpoint Tuesday at a Caterpillar factory (search) before gradually releasing them and surrendering.

No one was injured during the two-hour incident at the construction-equipment plant southeast of Raleigh.

The woman toted a shotgun and claimed she had explosives on her body when she walked into the plant's lobby in mid-afternoon, authorities said. Investigators found no evidence of explosives by early evening.

"Apparently, she is an acquaintance or friend of an employee terminated recently" and was "demanding answers," said Johnston County Sheriff Steve Bizzell (search). He described the woman as "irate about the treatment that her friend got."

The suspect, who was not a Caterpillar employee, was being taken to the Johnston County Jail, said sheriff's department spokesman Pat LaCarter. The woman's name was not immediately released.

"The thing we're thankful for is everybody's out, nobody's hurt," LaCarter said.

More than half of the plant's 800 to 900 employees were working at the time. They were removed on buses.

Authorities originally reported the woman had taken five hostages, but later corrected that number. The hostages — two women and a man — were in the lobby when the woman entered. They didn't know her, officials said.

Negotiators brought in the friend who had lost her job to talk with the hostage-taker, said State Bureau of Investigation agent Mike East. The friend said she was worried about the hostage-taker's safety.

"Once she talked to her friend, she was at peace and she was able to come out," East said.