Otago University students are being asked to stay alert and vigilant after a shooting threat was posted online earlier this week.

Dunedin students remain "on edge" despite a gun threat so far proving empty, while a second New Zealand university is evacuated over a bomb scare.

Police want University of Otago students to nominate potential suspects for the online threat towards the Dunedin campus. They are yet to identify the person who made the threat and what country it came from.

About lunchtime, part of Victoria University, in Wellington, was evacuated over a bomb scare.

Hamish McNeilly/Stuff.co.nz Inspector Mel Aitken fronts a press conference in Dunedin over threat made to Otago University campus.

Summer Cooper, of Christchurch, was the only one from her flat to go to the Dunedin campus on Wednesday.

Her flatmates chose to study at other libraries in the city as "everyone is just a bit freaked out".

Lectures were half full, and the normally busy central library was quiet.

JAMES GUNN/STUFF Police officers patrol the deserted Otago University campus after an online gun threat.

Ella Snedden, of Auckland, said the feeling was "sombre" around the Otago campus.

She was preparing for an exam on Wednesday, with the last week of lectures important before student exams.

"Everyone is a little bit on edge."

HAMISH MCNEILLY/STUFF The University of Otago resembles a ghost town after an online threat warning students to stay away.

The University of Otago has more than 20,000 students on its roll, including about 1200 international students.

Otago University Students Association president Paul Hunt was first made aware of the threat via social media.

"I think it was worrying because it is something that has happened overseas," he said.

The threat had raised anxiety levels around campus, but "we have confidence in police and having them on campus gives people a level of comfort".

He had a message to the person who posted the threat: "Get help".

The association, alongside the university, would offer support to any students with concerns, with lecture notes likely to be offered to those who missed classes.

POLICE PRESENCE

Uniform and undercover police have been stationed at the near-empty campus with officers parked in cars at the grounds on Wednesday morning.

Areas usually teeming with students were deserted. Some lecturers and support staff were understood to have stayed away.

Several students said normally packed lecture theatres were much quieter than normal.

Acting area commander Inspector Mel Aitken advised staff and students on campus to stay "alert and vigilant, but not be alarmed as we continue to look at the authenticity of this post".

Aitken told a media briefing on Wednesday morning that "copy cat" threats and prank calls after high-profile events overseas would be dealt with firmly.

Officers would maintain a visible presence at the university on Wednesday and hand out crime prevention advice, but otherwise it was "business as usual", she said.

Police would not divulge their tactics, nor comment on any progress of their investigation.

Investigators had been contacted by some members of the public, concerning people of interest.

"We are encouraging that. If there is anyone they think we need to know about we are certainly asking them to contact police."

The threat was posted by a person known as "NZ Robot" on an anonymous online message board on Monday night.

That threat, which included a picture of a gun, said "If you're in Dunedin, I wouldn't recommend coming to Otago University on Wednesday".

The person made reference to mass shootings and the gunman responsible for killing 32 people at Virginia Tech in 2007.

He signed off "see you in hell you magnificent bastards".

The thread has since been removed.

Police and the University of Otago were made aware of the threat on Tuesday morning.

SUPPORT OFFERED

The University of Otago has more than 20,000 students on its roll, including about 1200 international students.

Otago University Students Association president Paul Hunt said he was first made aware of the threat via social media, and "I think it was worrying because it is something that has happened overseas".

The threat had raised the anxiety levels around campus, but "we have confidence in police and having them on campus gives people a level of comfort".

He had a message to the person who posted the threat, "get help".

The association would offer support to any student with concerns, while the university was offering lecture notes to those who have missed classes.

A text sent by the university on Tuesday afternoon said: "A security threat has been made against the University of Otago (Dunedin campus) through social media. While the threat has not been substantiated at this time, it is being taken seriously."

The university was working closely with police and updates would be posted on its website as and when required, the message said.

Last week 10 people were killed in a shooting at a community college in Oregon.

Before the shooting an anonymous post on the 4Chan bulletin board said: "Some of you guys are alright. Don't go to school tomorrow if you are in the northwest."