Volunteers on board Marine Rescue NSW vessel Lemon Tree 30, responded to a Pan-pan call off Nelson Head on the NSW Hunter Coast where a catamaran had capsized.

Marine Rescue NSW Inspector Courtney Greenslade said radio operators at Marine Rescue Port Stephens took the initial call at 11.20am.

She said with Marine Rescue Port Stephens vessels committed to the search for a missing rock fisherman and other calls for assistance by boaters in the area, the Lemon Tree Passage unit was tasked for the rescue mission,

LT 30 was deployed at the request of NSW Police Marine Area Command who also attended the incident.

"Thankfully other boats were monitoring the sailors when the Marine Rescue NSW vessel arrived," she said.

"The three people were all sitting on the hull. They were all uninjured and safely returned to shore."

It's believed one of the hull on one side of the catamaran filled with water, forcing it to overturn.

The disabled vessel was secured and towed to Little Beach by Lemon Tree 30.

"The crew on board Lemon Tree 30 and our radio operators from both the Lemon Tree Passage and Port Stephens units worked seamlessly to complete a successful rescue mission," Inspector Greenslade said.

"The other vessels that monitored the people on the capsized catamaran should also be commended for keeping watch over the incident," she said.