Fellow diners were left in shock at Woolloomooloo on Monday afternoon when they witnessed high-profile businessman John Singleton, 73, lunging at his old friend and fellow millionaire Jack Cowin, 72, following a long lunch at upmarket restaurant Kingsleys steakhouse.

According to witnesses, Mr Singleton and Mr Cowin had been lunching together with musician Jon Stevens.

The lunch party arrived at Kingsleys at 1pm. It was after 4pm when onlookers saw Mr Singleton lunge at Mr Cowin, with staff at the restaurant attempting to separate the men.

"It looked like John was going after Jack. Jack was still sitting down and Singo was standing over him. We could see Jack was pushing him away. Singo really lost it, I think everyone was pretty shocked by what they saw," a witness to the fracas told PS.