He says New Jersey is seeing "small spikes in reinfection" from residents coming back from Florida, South Carolina and other virus hotspots.
"There was a wedding in Myrtle Beach and we absolutely have evidence of folks who were at that wedding who came back up to New Jersey, Jersey folks who were visiting there, and we've got other cases that we're running down," Murphy said.
Murphy spoke on NBC's "Meet the Press."
The governor also said the state is already seeing spikes as a result of the long IndependenceDay weekend.
Murphy noted that more than 13,000 New Jerseyans have died from complications related to COVID-19 and he said the U.S. is "only as strong as our weakest link right now."
"We went through hell, we cannot afford to go through hell again. We need a national strategy I think right now. And masking has got to be at the core of that," Murphy said.
Hoboken officials announced a spike in cases Saturday in which 12 of the 13 who tested positive Thursday and Friday went to states on New Jersey's travel advisory quarantine list.
When asked about his decision to delay the reopening of indoor dining, the governor said he sympathizes with restaurant owners and called for direct federal cash assistance to states so that they can help owners of struggling restaurants and small businesses.
"But the choice is either we open inside or, based on the data that we saw, and as I said the lethality of this virus inside, or we lose people, we literally lose lives," Murphy said.
New Jersey reported another 23 deaths associated with the coronavirus Sunday, bringing the statewide total of deaths confirmed to have been associated with the coronavirus and those considered probable to 15,211 - 13,355 confirmed by lab tests and 1,856 considered probable.
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