Murphy officials said they are watching a particularly concerning trend among new cases of COVID-19 in the state: A surge in young people aged 18 to 29.

In April, that age group made up 12 percent of new COVID-19 cases. Now that’s up to 22 percent, according to State Health Commissioner Judith Persichilli.

“While we know that some of this increase can be attributed to an increase in cases of testing, we are still concerned about this trend,” Persichilli said at the governor’s daily COVID-19 press briefing Tuesday afternoon at the Trenton War Memorial.

And reports of packed weekend gatherings at an outdoor restaurant in Morristown and a restaurant in Belmar were particularly worrying, according to the health commissioner.

“Individuals were packed together in these locations, which raises the risk of spreading COVID-19 to one another,” she said.

Many people in this age group who have the virus do not show symptoms, making a spread of COVID-19 all the more likely, she added.

Murphy has warned that should cases begin to creep up, he would ultimately put the breaks on a slew of reopenings planned through July 2, and  promising a crackdown on any such establishments that allow crowded, tightly packed gatherings to continue unchecked.

Some of the newer restrictions being lifted mean that indoor dining, casinos, and amusement and water parks can reopen at reduced capacity, and with added sanitization, social distancing and face coverings.

“There is absolutely no reason for our rate of transmission to begin to creep back up because people have become complacent in social distancing, or are crowding around bars and restaurants unmasked,” he said. “We can’t get our economy back to where it was if our hospitals fill back up with COVID-19 patients because some people mistakenly thought they were invincible.”

States such as Arizona, California, Florida, Nevada and Texas have undergone surges of new cases in recent weeks. Common denominators with flare-ups in these and other states, according to Murphy, has been young people and indoor activities.

The three big metrics that the Murphy administration uses to gauge the extent of the virus in the state are the rates of transmission, positivity and hospitalizations. Murphy said that should numbers trend in the wrong direction he would stop the reopening, but he has not indicated what specific numbers would trigger such a decision.

As of June 19, the positivity rate of tests was 1.96 percent, and the transmission rate was 0.81 percent. As of June 22, there were 1,092 COVID-19 patients in New Jersey’s hospitals.