Thousands of motorists have already been caught illegally using their phone while driving in the first week of the NSW Government's mobile phone detection camera program, and will now receive a warning letter in the mail.

"From Sunday 1 to Saturday 7 December, 3,303 drivers were caught breaking the law by fixed and mobile trailer-mounted cameras at various locations across the state," Minister for Roads Andrew Constance said.

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"Those drivers captured through 773,532 vehicle checks could count themselves lucky to be only receiving a warning letter.

"At 60km/h if you look at your phone while driving for just two seconds, you travel 33 metres blind - it's dangerous, it's stupid and it needs to stop.

"Around 500 drivers a day are getting pinged by these cameras doing the wrong thing. With double demerits starting Friday we need drivers to get the message and get off the phone, otherwise they risk killing themselves or someone innocent on our roads.

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"I'd like to thank drivers doing the right thing, we have seen a reduction in the noncompliance rate by two thirds since we first trialled the technology earlier this year."

When the warning phase ends in march 2020, drivers will cop a $344 fine, or $457 in a school zone, and five demerit points - 10 during double demerit periods.

Executive Director of Transport for NSW's Centre for Road Safety Bernard Carlon said what's needed is a "steep behavioural change from motorists to save lives".

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"While drivers caught on camera get a warning now, NSW Police will continue to issue fines for illegal mobile phone use as part of their regular operations," Mr Carlon said.

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