Northumbria University says 770 students have tested positive for coronavirus.
A spokesperson for the institution, based in Newcastle upon Tyne, said 78 students were displaying symptoms.
All of them are now self-isolating.
Flatmates and any close contacts are also going into quarantine, and have been advised to book a test if they develop COVID-19 symptoms, the spokesperson added.
In a statement, the university said it was supporting those affected by providing food and other essential items, such as laundry and cleaning materials.
It is also offering "welfare support including 24/7 online mental health support and one-to-one support from our wellbeing teams".
And it is "working together with our students' union, the City Council and other partners".
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But it warned that students who break coronavirus rules will be "subject to fines from police and disciplinary action by the universities (it and Newcastle University), which may include fines, final warnings or expulsion".
Students now confined to halls of residence will continue to learn remotely with "additional academic support in place to make sure they are not being disadvantaged" if they miss some face-to-face tuition.
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More than 50 UK universities have confirmed cases of coronavirus as students return to campus, according to analysis from the PA news agency.
Northumbria said it and its neighbouring university have "Covid Response Teams on call that are working closely with NHS Test and Trace" and local officials.
Students are being encouraged to download the NHS COVID-19 App.
Councillor Irim Ali, a cabinet member on Newcastle City Council, said the city and university had gone to "incredible lengths" to create COVID-secure environments for students but "sadly, a small number of students are undermining these efforts".
She added: "While work continues to control ongoing outbreaks, we need all students to comply with the regulations and guidance.
"If we are to beat the virus, we need a collective effort."
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