‘It’s going to get worse before it gets better,’ the Connecticut governor says as 3 cities add restrictions.

Months after Connecticut first began its reopening, its largest cities on Thursday announced plans to reimpose restrictions on businesses and gatherings as the state confronts a surge in virus cases.

Over the past week, Connecticut has seen an average of 725 cases per day, according to a Times analysis — more than double its average two weeks earlier.

On Thursday, Gov. Ned Lamont reported that the state’s average positivity rate in the last week was 3.1 percent — a rate not seen in Connecticut since early June, when the state first started opening up after a severe outbreak gripped the New York City region.

“I look hard to find a silver lining, and I can’t find it in these numbers,” Mr. Lamont said. “There’s no good news in those numbers.”

Earlier this month, the state released a color-coded plan to begin targeted shutdowns in the hardest-hit municipalities, which are labeled red. Thirty towns and cities are currently in red zones, meaning they must cancel public events and postpone indoor and outdoor activities where social-distancing or wearing masks is not possible.

Those municipalities are also allowed to roll back to an earlier phase of the state’s reopening plan, reducing the occupancy limits for many businesses and capping the size of private gatherings.

As of Thursday, three of the state’s largest cities — New Haven, Bridgeport and Stamford — said they would roll back their reopenings.

Mr. Lamont also said the state’s single-day positivity rate was 6.1 percent, its highest since June 1, which he viewed as cause for concern.

“This 6.1 may be a harbinger of things to come,” he said, later saying “it’s going to get worse before it gets better.”

Elsewhere in the region, Gov. Philip D. Murphy of New Jersey said on Friday that his state had reported 2,089 more cases of the coronavirus — the first time since early May that the state had reported over 2,000 new cases in a single day.

Newark, the state’s largest city, earlier this week imposed a curfew requiring non-essential businesses close by 8 p.m.