A man has been stabbed at a bus stop in the NSW Hunter region after getting into an argument with an unknown man.

Police said the victim, 24, and two women, aged 23 and 22, were waiting for a bus on Munro Street in Singleton when a man approached them about 3.45am (AEDT) on Saturday.

An argument ensued between the trio and the man, before a second man emerged from behind the bus shelter and stabbed the 24-year-old twice in the stomach.

The two unknown men fled and were last seen running down Munro Street.

The wounded man was airlifted to John Hunter Hospital where he remains in a serious but stable condition.

Police are appealing for information to identify the two men.