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.
Ellie Burgoyne, 19, a first-year social sciences student, said at least 20 flats in her halls of residence were now isolating.
She too is quarantining after one of her flatmates tested positive a week ago, and said it "isn't the most fun".
A member of staff, who wished to remain anonymous, said there were "high anxiety levels" about "face-to-face teaching".
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".
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.
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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Analysis: Fears student infections may spill over into community
By Rowland Manthorpe, technology correspondent
This big outbreak will raise further questions about the wisdom of reopening universities and colleges, not least because the risk of doing so was identified well in advance by the government's scientific advisors.
Minutes from the Scientific Advisory Group for Emergencies (SAGE) meeting of 1 September, released today, warn that opening further and higher education "has the potential to drive outbreaks".
Young people are much less likely to have severe coronavirus, but SAGE warns that transmission within universities and colleges may "spill over into the community".
The movements of students, the scientists say, means "the risk may be national".
But even though we have already seen outbreaks across universities, the biggest risk may yet be to come.
SAGE says larger outbreaks might leak into the community "towards the end of the academic term, coinciding with the Christmas and New Year period, when students return home".
Managing that will need, they note, "national oversight, monitoring and decision-making".
The decision has been made and students have gone to university.
But it's not at all clear how they will be able to leave.