A teenager has died after he was stabbed at a social gathering at a home on the New South Wales south coast.

Police went to West Birriley Street, Bomaderry after a teenager had "suffered chest injuries" about 7pm.

The 18-year-old was taken to Shoalhaven Hospital in a critical condition but died a short time after his arrival.

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Neighbour Gage Hood said there was a bit of a gathering happening but he didn't realise anything was wrong until he saw the police cars.

"The story was someone fell on a knife but you don't fall on a knife," Hood said.

Acting inspector Ian Griffin said all of the people at the "gathering" knew each other.

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"It is a terrible set of circumstances but there is certainly nothing in our investigation that should concern the community and we will continue to try and find out what has occurred," Griffin said.

He confirmed it was a single stab wound that killed the teenager.

Police are asking anyone with information to contact Crimestoppers on 1800 333 000