A man has died after two boats collided on Sydney Harbour.

Emergency services were called to New Beach Road in Darling Point following reports of an accident at about 6:30pm on Friday.

Officers along with the Marine Area Command found a man believed to be in his 50s with severe chest injuries.

NSW Police said the man, who is yet to be formally identified, died at the scene.

"Both skippers will be subject to mandatory testing," police said in a statement.

"And both vessels have been seized for mechanical examination." 

Investigations into the incident are underway, with detectives at the scene late into the night.

A report will be prepared for the coroner.