The CEO of Britain's Compass Group CEO, Richard Cousins, was among six people who died after a seaplane crashed into a river in Sydney on New Year's Eve.

The other five who died in the crash were his fiancee Emma Bowden, 48, her daughter Heather Bowden, 11, Edward Cousins, 23, William Cousins, 25, and the 44-year-old pilot Gareth Morgan, Detective Superintendent Mark Hutchings from the New South Wales Police said.

Police are working with the Australian Transport Safety Bureau to recover the wreckage of the plane, which is submerged in 13 metres of water near Cowan, north of Sydney.

An investigation into the cause of the crash has begun, with a preliminary report expected within 30 days. Authorities have warned that it may take up to a year to find out what happened.

Police say the plane was returning a party of five passengers from a wine and dine experience in the city's north to Rose Bay when it crashed, sinking immediately.

The seaplane was part of the Sydney Seaplanes business, which has operated since 2005 with no previous record of mishap. Seaplane flights have been cancelled until further notice.

Compass chairman Paul Walsh said in a statement: "The thoughts of everyone at Compass are with Richard's family and friends, and we extend our deepest sympathies to them."

"Richard was known and respected for his great humanity and a no-nonsense style that transformed Compass into one of Britain's leading companies," he added on Monday.

Cousins, who led Compass - the world's biggest catering firm - over the past 11 years, was due to step down in March. It followed his decision to quit his role of senior independent director of supermarket giant Tesco.

He has been widely credited with turning the company's business around and making Compass into one of the Financial Times Stock Exchange's best-performing firms.

Cousins had also been named as one of the world's best-performing CEOs by Harvard Business Review.