The NSW Government's world-first mobile phone detection cameras have been operating in warning mode since December 1, 2019, but drivers caught doing the wrong thing will now cop a $344 fine and five demerit points.

Minister for Roads Andrew Constance said nine million vehicles had been checked by the cameras during the three-month warning period, with more than 30,000 warning letters issued to offending drivers.

"We're seeing more than 99 per cent of drivers doing the right thing, so when we compare this with the findings from the pilot last year, it is clear drivers are starting to get the message.

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"As fines and demerits start to be issued from today we expect the number of offences could fall even further, making NSW roads safer for everyone.

"It's important that drivers who continue to put the safety of themselves, passengers and the local community at risk realise that no matter where you are you could be caught and you will be fined," Mr Constance said.

Minister for Regional Roads Paul Toole said taking your eyes off the road for longer than two seconds doubled the risk of a crash.

"The decision to pick up your phone can have fatal consequences. Whether you're driving on a major highway or an isolated road in the bush, there's no excuse for using your phone illegally," Mr Toole said.

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"The cameras are both fixed and transportable, with the trailer-mounted cameras to be frequently moved around the state, targeting illegal mobile phone use anywhere, anytime."

NSW Police continue to enforce illegal mobile phone use and issue infringements as part of regular operations.