Flynns Beach has been closed after hundreds of bluebottles appeared in the water and washed onto the shore.
Lifeguard supervisor James Turnham said the decision was made to close the beach after a few people were stung by the marine creatures.
Mr Turnham said bluebottles at the beach was nothing too out of the ordinary and often happened with a north-easterly wind.
He said he expected the beach would be reopened tomorrow, depending on tide changes.
Surf Life Saving NSW first aid treatment advice for bluebottles is to wash off any remaining tentacles with seawater and immerse the patient’s sting in hot water (no hotter than can be easily tolerated).
The application of cold packs or wrapped ice is also effective.
Port Macquarie Surf School instructor Wayne Hudson said this is the first time that he knows of that the beach has closed due to bluebottles.
The surf school has been running since 1981.
Mr Hudson said bluebottles usually come in three or four times a year.