The Middlesex London Health Unit has declared a COVID-19 outbreak at a popular London pizza place after four staffers tested positive for the coronavirus.

Piero's Pizza is located at 169 Wharncliffe Road South.

The health unit was initially told about a case at the business on Jan. 19, and additional cases on Jan. 22. Three of the sick staff members worked while they were infectious, the health unit said in a statement.

"After investigating these new cases, the health unit has determined that transmission of COVID-19 has likely occurred at the store and for that reason has decided to declare an outbreak," officials said.

"Although the employees have indicated that they wore masks while they were at work and that there is a plexiglass barrier between customers and staff at the business, there may have been a low-risk exposure for some customers."

Customers who visited Piero's or had pizza delivered between Jan. 15 and Jan. 19 should monitor for COVID-19 symptoms. Those who have symptoms should get tested at one of London's COVID-19 assessment centres.