NSW police say their brand new flood rescue fleet will help back up rescue missions but will also be used to round up anyone looting or breaking the law.

Devastating flooding across the state last summer resulted in the death of a man in Grafton and a 17-year-old boy who was sucked into a drainpipe as he collected golf balls in Port Macquarie.

Launching the six new boats in Sydney on Tuesday, NSW Police Marine Area Commander Mark Hutchings said that as well as backing up SES rescue operations, they would be used to maintain order in emergency situations.

"Sometimes we get reports of people looting etcetera, so our boats are out there ... so they can actually go out there and do arrests," he told reporters.

The Bureau of Meteorology is not warning emergency services to expect bad flooding but Mr Hutchings' command is preparing for a worst case scenario.

"We assume we are going to get a flood and we're ready trained and ready to respond," he said.

Police Commissioner Andrew Scipione said the new boats "may well be the boats that will come and rescue you should you be unfortunate enough to be caught in a flood".

The boats replace older vessels that were made more than 30 years ago.