NORWALK — Mayor Harry Rilling is in quarantine due to close contact with someone who has tested positive for COVID-19, city spokesman Josh Morgan confirmed Sunday.

Rilling entered quarantine Oct. 16 after being in contact with family who later tested positive for the novel coronavirus, Morgan added.

The mayor has since tested negative twice, Morgan said, but “will continue to quarantine in accordance to public health guidelines.”

News of Rilling’s quarantine comes amid increasing cases of COVID-19 in Norwalk, resulting in the city being classified as in a “red zone” by state health officials. That level is reached when a municipality has more than 15 positive cases per 100,000 residents over a two-week period. Between Oct. 4 and 17, Norwalk reported 18.9 cases per 100,000 residents.

While Gov. Ned Lamont has empowered mayors in red zones to revert to revert to Phase Two of the reopening process — reducing capacity for indoor establishments — Rilling held off this week on cutting capacity at local businesses.

“We’ve been staying on top of the case trends and saw this increase coming. That’s is why we proactively implemented the state’s recommendations for communities in a red-alert level well before this notification,” Rilling said in a release Thursday. “We have upped our testing, sent out more community messages, and discouraged public events and non-essential trips.”

Norwalk is one of 19 communities in Connecticut listed as “red alert,” up from 11 last week. There are another 21 communities in the “orange alert” category, 10 to 14 cases per 100,000 people, up from 14 municipalities last week.

Three Fairfield County towns — Norwalk, Fairfield, and Danbury — are red-alert towns. Wilton and Stamford are both in the “yellow zone,”, reporting five to nine cases per 100,000 people.

The increase in COVID-19 cases is coming as more schools return to in-person learning, and with Halloween coming Saturday.

“This is a serious situation and we must remain vigilant,” Rilling said. “I am asking for the public’s help to slow this virus down. Please avoid parties and gatherings, always wear a face covering, and keep your social distance.”