An “armed and dangerous” suspect remains at large in Vermont after a woman's body was discovered on a popular trail Thursday afternoon, prompting a large manhunt, urgent warnings to residents and the closure of Vermont State University's Castleton campus.

A passerby came upon the woman's body along the Delaware and Hudson Rail Trail in Castletown, about 30 miles south of Middlebury, and reported it to police, who arrived at the scene around 4:30 p.m. Thursday, according to the Vermont State Police.

A witness in the area told investigators they heard gunshots and saw a possible suspect walking toward the Vermont State University Castleton campus, less than a mile north of where the incident occurred.

Vermont State University president says situation is 'deeply unsettling'

The university issued a shelter-in-place warning Thursday evening, according to the university's website. The campus canceled all events for Friday and extended the shelter-in-place warning, citing the "ongoing investigation."

"We ask all employees and students not to travel to the Castleton Campus for any reason," read a statement by Michael Smith, the interim president of Vermont State University, adding: "This situation is deeply unsettling."

Vermont State Police Maj. Daniel Trudeau refused to name the victim but said she was not a student at the university during an update at a news conference Friday afternoon. He said investigators were waiting for an official cause of death from the Medical Examiner's Office. The case was being treated as a homicide.

Vermont State Police: 'We need a good first clue'

At the news conference, Trudeau described the suspect as a white male, approximately 5 feet 10 inches tall, with short dark-colored hair. The man was last seen wearing a dark T-shirt and carrying a black backpack, he said.

Trudeau said police do not have a name or any more information about the suspect other than the descriptions provided by witnesses.

"We need a good first clue," he said before calling on residents to provide relevant tips and surveillance footage.

A statement from Vermont State Police described the suspect as "armed and dangerous."

Investigators canvass nearby Castleton homes in manhunt

Police began canvassing houses in the area around where the woman was found Thursday night and continued into Friday afternoon. Residents have been urged to keep the doors of their cars and homes locked and to stay aware of their surroundings.

"As the search continues for a suspect, please make phone calls to friends and family in the area to check in on them," the town of Castleton said in a Facebook post. "If going into buildings or outbuildings that are not/have not been locked, use the buddy system, meaning have another person with you, and have a cell phone with you whenever possible."

Police cordoned off the street near where the woman was found and closed the trail.

The investigation is being headed by the Vermont State Police's major crime unit in conjunction with the Castleton Police Department.

The Delaware and Hudson Rail Trail is a 19.8-mile section of former railroad that cuts through through scenic countryside with vistas of the nearby hills, villages, farms, fields and forests, according to its website. It's a multiple-use trail open to pedestrians, bicyclists, and horseback riders in the summer, and snowshoers, skiers and snowmobiles in the winter.