Multiple cases of the omicron coronavirus variant have been detected in New York, health officials said Thursday, including a man who attended an anime convention in Manhattan in late November and tested positive for the variant when he returned home to Minnesota.

In addition to the conventioneer who was vaccinated for COVID-19, government officials said tests showed five other people recently infected with the virus had the variant. They included a person in the city's Long Island suburbs who had recently traveled to South Africa, residents of Brooklyn and Queens and another case possibly linked to travel. At least one person had received a dose of a COVID-19 vaccine but officials did not have details about the vaccination status of the four other cases.

Gov. Kathy Hochul at said at a news conference with New York City Mayor Bill de Blasio that officials were still gathering details on the cases but there was “no cause for alarm."

"We just want to make sure that the public is aware of information when we receive it,” she said.

De Blasio said the geographic spread of the positive tests suggested the variant was undergoing “community spread” in the city, and wasn’t linked to any one event.

“We gotta assume there’s a lot more behind that and that it has been here for a meaningful amount of time," he said.

The news came a day after the U.S. announced its first known case of the variant had been detected in California, in a person who had recently traveled to South Africa.

Officials reported another case Thursday in a Colorado woman who had recently traveled to southern Africa.

The Anime NYC 2021 convention Nov. 19-21 drew about 50,000 people, according to event organizers, and attendees were required to wear masks and show proof of having received at least one dose of a COVID-19 vaccine.

The man who attended the event had not traveled outside the U.S. and began experiencing symptoms the day after the convention, which Minnesota Health Commissioner Jan Malcolm said made it “perhaps the most likely,” that the man contracted COVID-19 at the New York City convention, but officials did not know for sure.

Officials in New York said they were working to trace attendees of the convention, which was held at the Jacob K. Javits Convention Center as New York City prepared to host the annual Macy’s Thanksgiving Day Parade and braced for throngs of tourists to return after the U.S. opened up to vaccinated international travelers.

Officials in the city of 8.8 million said they expected it would be only a matter of time before the new variant was reported in the city. City Health Commissioner Dave Chokshi urged people who attended the event to get tested.

"This is not just due to people who are traveling to southern Africa or to other parts of the world where omicron has already been identified,” Chokshi said Thursday.

The Minnesota man began experiencing mild symptoms Nov. 22. He had been vaccinated and received a booster shot in early November, according to health officials in his home state. He sought COVID-19 testing Nov. 24, and his symptoms have subsided, officials said.

Nov. 22 was the same day the person infected in the California case returned to the U.S. from South Africa. The California traveler, who was vaccinated, developed mild symptoms and tested positive Monday.

Much remains unknown about the new variant, including whether it is more contagious, as some health authorities suspect, whether it makes people more seriously ill, and whether it can thwart the vaccine.

Omicron is classified by the World Health Organization as a “variant of concern” as scientists work to determine how it may compare with the predominant delta variant in terms of transmissibility and severity. Scientists also are studying the degree to which existing vaccines and therapies protect against omicron.

Scientists in South Africa first reported it, but the samples came from several countries in southern Africa. And health officials in the Netherlands now say it was found there prior to the South Africa detection.

As comfort over air travel returns, it’s inevitable that new variants like omicron will spread from country to country and state to state, said professor Danielle Ompad, an epidemiologist at New York University’s School of Global Public Health.

“We shouldn’t panic, but we should be concerned,” she said.

Hochul said the case involving the Minnesota visitor underlined the need for everyone who is eligible to get vaccinated against COVID-19 or receive a booster shot if they have not already.

“There is one way to address this - New Yorkers, get vaccinated, get boosted, and get ready,” the Democrat said.