A manhunt was under way in Pennsylvania Wednesday for a man police say threatened two nurses at gunpoint at a mental health care facility then took off with his girlfriend, who was a patient.

Elliot Ravert, 18, allegedly demanded nurses at Philhaven unlock the housing unit were Alicia Buzzard, 21, was a patient and threatened to shoot them if they did not cooperate with his demands, police said.

Authorities were unsure if Buzzard went willingly with Ravert, but they issued a missing-person alert for her and said she might be at risk of harm. She had been at the hospital for about a week and a half.

None of the hospital staff were injured.

Tiffany Buzzard, Alicia’s sister, told Lancaster Online that their mother had asked hospital officials to not allow Ravert to see his girlfriend.

An arrest warrant was issued charging him with aggravated assault, terroristic threats and robbery. Police said he took a two-way radio from the hospital.

Buzzard has bipolar disorder and has known Ravert for about three months, his sister said. She lives in Myerstown, about a half hour from the hospital, with her mother and stepfather.

"My mom and stepdad separated her and Elliott because they were starting to get physical and trying to have babies," Tiffany Buzzard told Lancaster Online. "She stopped taking her medicine and threatened to kill herself."

According to the website, Buzzard and Ravert met three months ago at an intermediate school. The relationship was fine at first, but Jacqui Shay, Buzzard’s mother, said it turned violent quickly.

Shay said Ravert became “obsessed” with knowing where Buzzard was at all times. Shay told Ravert not to date her daughter anymore.

“I believe he was filling her head with marrying her, having kids, that he would fight us for her," she said. “He would be the knight in shining armor coming to rescue her.”

Both families are cooperating with the investigation.

Ravert drives a green 2004 Chevy Avalanche with Pennsylvania license plate ZGY-3594, but police said late Wednesday he may have changed plates.

Authorities said they did not know where Ravert might be headed.

The Associated Press contributed to this report.