London's public health unit has declared an outbreak inside a residence building at Western University, moving some students into an undisclosed quarantine location.

The Middlesex London Health Unit said Sunday night that four students living in London Hall, on Western Road south of the university gates, had tested positive.

"Declaring an outbreak is an important step in addressing any further spread of COVID-19 within the Western student community," Dr. Alex Summers, Associate Medical Officer of Health with the Middlesex-London Health Unit, said in a statment.

Close contacts to the infected students have been contacted, Summers said.

In a written statement released shortly after the health unit declared the outbreak, Western University said the infected students have been moved out of residence, and out of "an abundance of caution" has also moved close contacts to quarantine.

"We are delivering them meals, and our staff are in regular contact to ensure students are well supported," the university said.

MLHU made a point of reminding students to not visit the GTA, Ottawa and other hot spot locations.

It may be a warning that comes too late, with many students having already travelled home for Thanksgiving.

Sunday saw the largest single-day increase in the region since April, with 20 new cases recorded.

MLHU said 13 of Sunday's new cases are people in their 20s or younger.

Western University is reminding students that the on-campus testing site is open starting Tuesday for anyone with symptoms