Bangor will go into lockdown this weekend, the Welsh Government has announced.
Eight wards in the city - Garth, Hirael, Menai, Deiniol, Marchog, Glyder, Hendre and Dewi - will have further Covid-19 restrictions from 18:00 BST on Saturday.
The restrictions will be similar to those in other counties across Wales.
Residents will not be allowed to leave or enter the areas without a reasonable excuse and can only meet outdoors.
The Pentir ward, which includes parts of Penrhosgarnedd and is the site of Ysbyty Gwynedd, is not covered by the restrictions.
The Welsh Government said Bangor had seen a significant cluster of cases and the incident rate stands at about 400 cases per 100,000 people.
It said cases are appeared to be closely associated with young people and the student population.
First Minister Mark Drakeford said the cases were "largely linked to people socialising".
He added that although large parts of Wales are currently under further local restrictions, "this is not a national lockdown".
"These are a series of local restrictions to respond to rises in cases in individual areas," he said.
"It's always difficult to make the decision to impose restrictions but we hope that these measures will make help to control the spread of the virus."
Leader of Gwynedd council, Dyfrig Siencyn, said: "Acting now will help slow the rapid increase in positive cases in the city, break the chain of transmission and protect Bangor residents as well as the wider Gwynedd public."
He said the council appreciates the impact lockdown will have on people and businesses.
But taking these steps now will hopefully mean avoiding "stricter and more disruptive measures further down the line".
He added that there was no room for complacency for residents across Gwynedd, even though the current lockdown only affects Bangor.