Hundreds of students at Northumbria University are self-isolating after testing positive for Covid-19.
A spokesman for the university, in Newcastle, confirmed 770 students had tested positive since returning in mid-September, 78 of whom are symptomatic.
All infected students, and their close contacts, have self-isolated for 14 days in line with government guidance.
Meanwhile, Newcastle University confirmed it has had 94 students and seven staff test positive.
A Newcastle spokeswoman said the "overwhelming majority of cases" were from "social and domestic settings".
University and College Union (UCU) said it warned Northumbria University it was "far too soon for a mass return to campus".
In a statement the UCU, which represents lecturers, said: "We told Northumbria University they had a civic duty to put the health of staff, students and the local community first and we take no pleasure in now seeing another preventable crisis play out.
"We warned last month that, given the current restrictions in the region, the direction of the infection rate and the problems with test and trace, it was clearly far too soon for a mass return to campus."
Northumbria University said self-isolating students were being provided with food, laundry, cleaning materials and welfare support by the university, working alongside the students' union and Newcastle City Council.
Ellie Burgoyne, 19, who studies social sciences, has been isolating since one of her flatmates tested positive a week ago.
She said: "The uni and accommodation have been great in providing support and keeping us as comfortable as possible as not leaving our flat for two weeks isn't the most fun.
"I moved a couple of weeks ago and immediately noticed how strict our accommodation was being when it came to students meeting with other flats, trying to have parties.
"I think it's a common misconception that students haven't been listening to the guideline, my accommodation has been quiet aside from the odd flat having a few people over."
'Surge in induction week'
Meanwhile, students will also receive additional academic support if they miss out on face-to-face tuition during their isolation period.
The university spokesman added: "The increase in numbers comes in the week after students returned to university and reflects the good access to and availability of testing, as well as rigorous and robust reporting systems.
"In parts of the UK where universities started term earlier, numbers of student cases surged in induction week, and then reduced.
"We are making it clear to students that if they break the rules they will be subject to fines from police and disciplinary action by the universities which may include fines, final warnings or expulsion.
"Both Northumbria and Newcastle universities have Covid response teams on call that are working closely with NHS Test and Trace, Public Health England North East and the City to identify and get in touch with anyone who has been in close contact with those affected."
Around 56 universities across the UK have had at least one confirmed case of Covid-19.
There have been more than 200 cases at the University of Sheffield and 177 University of Liverpool staff and students have tested positive, according to a PA news agency survey which contacted 140 institutions.
Approximately 2,500 positive cases of Covid-19 have been identified at these universities, the analysis suggests.
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