The scientists wrote in the journal Proceedings of the National Academy of Sciences that the new flu strain, which the researchers call G4 EA H1N1, is similar to the 2009 swine flu, but with some new changes, the BBC reported on Tuesday.
They found evidence of recent infection, carried by pigs, was starting in people who worked in abattoirs and the swine industry in China.
The researchers were concerned that it could mutate further so that it can spread easily from person to person, and trigger a global outbreak.
While it is not an immediate problem, they said that it has "all the hallmarks" of being highly adapted to infect humans and needs close monitoring.
The scientists further said that measures to control the virus in pigs, and the close monitoring of swine industry workers, should be swiftly implemented.
Professor Kin-Chow Chang, who works at Nottingham University in the UK, told the BBC: "Right now we are distracted with coronavirus and rightly so. But we must not lose sight of potentially dangerous new viruses."
While this new virus is not an immediate problem, he says: "We should not ignore it."
Professor James Wood, head of the Department of Veterinary Medicine at the University of Cambridge, said the work "comes as a salutary reminder" that we are constantly at risk of new emergence of pathogens, and that farmed animals, with which humans have greater contact than with wildlife, may act as the source for important pandemic viruses.
The last pandemic flu the world encountered - the swine flu outbreak of 2009 that began in Mexico - was less deadly than initially feared, largely because many older people had some immunity to it, probably because of its similarity to other flu viruses that had circulated years before, said the BBC report.
That virus, called A/H1N1pdm09, is now covered by the annual flu vaccine to make sure people are protected.
The development comes as the world is still struggling to contain the COVID-19 pandemic that originated in China's Wuhan city last December.
As of Tuesday, the virus has infected a total of 10,302,867 people globally, while the death toll stood at 505,518.