The fundraising event was at Trump National Golf Club in Somerset County just hours before Trump tested positive for coronavirus.
As many as 300 people attended the Trump event, according to NJ Advance Media.
New Jersey's governor announced that contact tracing to gauge the extent of COVID-19 exposure was underway.
In a tweet on Friday, Murphy also asked everyone who attended the event in Bedminster to self-quarantine.
Thursday's Somerset Hills fundraising event went forward even after White House officials confirmed that one of Trump's closest aides, Hope Hicks, a native of Greenwich, CT, tested positive for COVID-19.
Trump spoke to supporters wearing masks outside and held a meet-and-greet with major donors inside the country club.
At a Friday press briefing, White House Chief of Staff Mark Meadows told reporters: "We discovered that right as Marine One was taking off yesterday," referring to when they learned that Hicks had tested positive. Trump went to the indoor fundraiser nonetheless. Meadows said some people were pulled off the campaign trip.
Trump arrived at Morristown’s airport about 2 p.m. Thursday before taking a helicopter to Bedminster. He choppered back to Morristown and left New Jersey about 4:40 p.m.
News that Trump and First Lady Melania Trump contracted the virus grabbed worldwide headlines and rattled stock market trading 32 days before Election Day.
“Tammy and I send our best wishes to President Trump and First Lady Melania Trump for a speedy and complete return to good health," Murphy said in a Friday statement. “If there is one thing we have learned in New Jersey over these months, it’s that we pull together and support everyone fighting this virus.”
Why wasn't the president subject to the same out-of-state travel restrictions as ordinary citizens? Read the nj.com explanation here.
ALSO SEE: President Trump's personal physician says he can fulfill duties while in White House quarantine.
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