A 51-year-old McLean woman is being held at an undisclosed mental health facility after she allegedly made bomb threats aboard a Red Line train Monday morning, transit officials said.

Passengers fled the train, and some riders evacuated onto the track bed, eyewitnesses said.

“It was like a stampede,” said Michael Robb, 25, of Gaithersburg, who was aboard the train with his girlfriend. “Nobody could get off. People lost their shoes jumping onto the side of the tracks.”

Authorities closed the Rockville Station for about two hours while K-9 units and other teams searched for explosives. No explosives were found, Metro said, and there were no serious injuries. Passengers were bused to other Metro stops, and delays caused chaos for Red Line riders.

The inbound eight-car train with 250 to 300 passengers was leaving the Rockville Station when a woman in a rail car near the front “got down on her knees” and said: “You killed my family. Now I’m going to kill you all,” Metro Transit Police Deputy Chief Ron Pavlik said at an afternoon news conference.

Metro Transit Police withheld the suspect’s name because she is undergoing a mental health evaluation and has not been charged.

When they heard the woman, passengers pressed the call button for the train operator and one rider called transit police, Metro officials said.

“I was scared to the max,” Robb said. “I’ve never seen anything like this. It was a total crisis on the train. . . . I was asking people, ‘What happened? What happened?’ They were just saying, ‘Move! Move! Just run!’

“We thought it was a terrorist attack the way people were moving and screaming,” he said. “I didn’t ask any more questions. I just jumped off and ran.”

The operator stopped the train and walked back to see what was going on, according to Metro officials and riders. Seven of the rail cars were no longer at the platform.

Metro authorities said the train operator followed proper protocol and called in the alleged bomb threat to Metro’s central control.

Metro Transit Police were immediately called to the scene, officials said, but panicked passengers used the emergency-release levers to open the train doors manually, jumped onto the track and began walking toward the Twinbrook Station.

The train operator realized riders were on the track and called Metro’s operations center. The power was quickly shut down, said Metro spokesman Dan Stessel.

Metro officials said about 35 people walked along the track. Other passengers walked back to the one rail car that was still in the station and exited onto the platform, Metro officials said.

On the outbound track headed to Shady Grove, a handful of passengers were stranded for about 45 minutes when the power was shut down, Metro said. Deborah Kalb, who was headed to jury duty on the train, said they were given few details of what was going on but could “hear dogs barking and sirens going and helicopters circling overhead.”

A few passengers were treated for heat-related complaints and were evaluated at the scene. They declined further medical treatment, Metro said.

Authorities said they think the female suspect evacuated the train through the last car, along with other customers, and walked onto the station platform. Metro officials said riders pointed out the suspect, who was apprehended in the Rockville “Kiss and Ride” area without incident by Transit Police and an officer from the Federal Protective Service.

The woman was taken into custody and transported to Shady Grove Adventist Hospital, where she underwent a mental health evaluation. By mid-afternoon, Stessel said the woman had been “involuntarily committed” and transferred to a facility “that has better resources to handle mental health issues.”

Metro Transit Police said they are not permitted to talk to the woman while she is being held for observation and have been “unable to get additional information about what the woman meant when she said, ‘You killed my family.’ ”

Stessel said in an e-mail that the woman is not a U.S. citizen. She has a “permanent resident card for the U.S., but an Indian passport,” he wrote.

Some riders complained that they were confused about what was happening during the morning commute, and did not hear the announcements or receive e-mail alerts about delays.

Other riders thought the situation went well, given its seriousness.

Bryn Gibson, another rider on the Red Line train, said she gave “a lot of credit to the conductor.”

“She came back and made sure everything was okay,” Gibson said. “She communicated they were working on things and making an effort to get us off.” Gibson said the shuttle buses worked well.

“They did a great job maintaining calm, and no one got hurt,” she said.

Last fall, two men were arrested in separate incidents arising from bomb threats against the Washington Metro system.

In one case, Farooque Ahmed, a naturalized U.S. citizen born in Pakistan, pleaded guilty in U.S. District Court to two terrorism-related charges and was sentenced to 23 years in prison.

Stessel said Monday’s bomb threat “was clearly an isolated incident from someone who appears to need mental health treatment, and any increase in security would not be warranted under this instance. We have no reason to believe this is anything more than an isolated incident.”

Staff writer Amy Orndorff contributed to this report.