About 1,700 university students have been told to self-isolate after 127 tested positive for Covid-19.
Students at two Manchester Metropolitan University accommodation blocks have been told to stay in their rooms for 14 days, even if they have no symptoms.
Students said "police and security were outside" and self-isolation had "left morale really low".
A university spokesman said disciplinary action will be taken against any breaches.
The restrictions affect students in accommodation blocks at Birley campus and Cambridge Halls after "127 students have tested positive with a number of others symptomatic or self-isolating", Manchester City Council said.
Students across the city have been urged to attend virtual freshers' events and avoid big parties.
But some said they had no warning of a lockdown and are now trapped in halls of residence.
Megan Tingy, who studies at Manchester Metropolitan, said on Friday "We were getting ready to go out and looked out to security and police outside the halls. They say we can't leave.
"We haven't received any emails from university about this and they seem to be holding us in against our will."
Student Trisha Kakooza, who is from London, said: "We had eight hours to go get food to last us for two weeks.
"We have to get any other food delivered, which is expensive.
"I have a job and it helps me make extra money since student finance isn't enough but now I can't go out to work.
"We can study remotely but I won't get paid by the agency I work for."
Chip Wilson, 19, said: "We have been told we are not allowed to leave and, if we do, we cannot come back, so now we are all stuck inside.
"On top of all this, many of us here have Covid symptoms but we cannot get tests. We can only get drive-through tests and none of us have cars, and even if we did we can't leave now."
Most parts of Greater Manchester have been subject to stricter restrictions since July after a spike in coronavirus cases.
The rate has also doubled in the city of Manchester to 1,026 positive tests in the week up to 22 September, compared to 515 cases in the previous week.
The lockdown comes as students in Scotland were told not to go to pubs, parties or restaurants this weekend in to stem the spread of the virus.
Joe Barnes, who recently started at Manchester Metropolitan University, told BBC Breakfast that self-isolation had "left the morale of my flat really low".
He said lessons were being conducted online "so theoretically I could go and study from home but that defeats the point - I've not just come for my studies but to meet new people and enjoy the experience."
He added: "I've heard horror stories of massive parties in some of the halls around here… it is just frustrating that no one else could have foreseen that."
The National Union of Students said affected students should be able "to return to their families if they wish, as being trapped in university accommodation will only add anxiety at an already difficult time".
"All students affected must be supported by their universities with food deliveries, shopping and access to mental health services if needed," a spokesperson said.
Jo Grady, general secretary of the University and College Union, said the Manchester incident was "the latest catastrophe in a week where wholly predictable - and predicted - Covid outbreaks have caused havoc on campuses across the UK".
"We warned last month of the problems with moving thousands of students across the country and the time has come for urgent action from ministers and universities to protect staff and students."
She urged university leaders to drop face-to-face classes until the government improves the test-and-trace system.
A university spokesman said: "We are fully supportive of the [lockdown] decision.
"Services such as wellbeing support and the library will remain available to our students online.
"Our security teams will increase patrols to support the lockdown and we will take disciplinary action against any students found to have breached requirements."
Councillor Bev Craig, executive member for adult health and wellbeing for the city council, said: "We understand that local residents may be concerned about this situation.
"We want to reassure them that the evidence so far suggests that transmission has been within the student community only and has not been more widespread."
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