Students who might be at risk have been sent letters

Vaccination sessions were arranged for students on Thursday after six cases this month.

The National Public Health Service expects further cases before Christmas, said the university.

Lectures in the school of education and student placements on teaching practice have also been cancelled.

Vaccines are being offered to up to 500 students on the Coleg Normal site, including those at the school of education and school of health and sports science.

A university spokeswoman said students at the site had been sent a letter "to inform them what they can do to protect themselves and help prevent the spread of mumps".

Students born after 1980 who have not received two doses of MMR (measles, mumps and rubella)vaccine have been advised to have a dose of the vaccine now.

MUMPS FACTS About one in three cases show no signs of illness but are still infectious Most cases get better in around a week to 10 days Inflammation and testicular pain occur in about 20% of male cases and may result in testicular atrophy Meningitis, one-sided deafness, sterility and pancreatitis are rare complications Mumps is very rarely fatal Source: National Public Health Service

Dr Richard Roberts, consultant in communicable disease control in the National Public Health Service for Wales, said "Mumps is usually an unpleasant but mild infectious disease, but with rare complications.

"Mumps usually causes pain then swelling of one or both saliva glands between the ear and the neck. This is usually accompanied by a fever and feeling generally unwell.

He said that the illness appears two to four weeks after exposure to an infectious case of mumps, and cases are infectious for up to a week before and a week after the swelling appears.

Matt Jarratt, of the students' union, said: "People will obviously be concerned but we've been assured by the university that they are doing all they can to prevent it from spreading."

There are around 10,000 students at Bangor but the university could not confirm how many had been sent letters, but said they were those studying or living on the one site.

There have outbreaks of the disease reported in other parts of the UK in recent weeks.