A record number of drivers have been caught paying more attention to their cellphones than to the road.

Police say a West Aucklander with a beer in one hand and a phone in the other was among the 4195 drivers caught and fined a total of $331,680 during a crackdown in September.

The latest police figures show a more than threefold increase in the number of drivers caught nationwide on their phones that month, compared with the average monthly numbers.

In the entire Auckland region, 1932 drivers were caught on their phones in September, compared with 963 in August.

The number of Wellingtonians snapped increased 75 per cent to 273, and the number of Cantabrians caught almost doubled, with 830 drivers fined.

Road policing national manager Superintendent Steve Greally said the figures were horrifying. "People are just flouting it. They don't understand the risk of taking your eyes off the road even for just two seconds.

"Even for just a second, you could kill a cyclist, another driver – even yourself. It's a huge issue for us."

Greally said he understood how drivers idling in gridlock or at a red light might think it was safe to use their phones, but it was illegal because it was risky.

"Even if you're going 5 or 6 kilometres per hour, you're going to cause a nose-to-tail. Or a small child might run out in front of you who doesn't know any better."

He said officers had not been given quotas during the two-week September sting, but all officers, including detectives who did not usually do road policing, were asked to pull over drivers on cellphones when they spotted them.

Breaking the rules results in an $80 fine and 20 demerit points. If 100 points are accumulated within two years, drivers automatically lose their licences for three months.

Greally said he was unaware of anyone who had lost their licence purely for repeated phone offences, but thought it likely.

"With technology, you've getting a lot more things that you can do with your phone.

"They are not just used for calling or for texting. It's apps – the more that increases, the more we'll be having people using phones while driving."

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The Automobile Association congratulated police on the crackdown, saying multi-tasking impaired drivers' judgment.

"There's no doubt it takes your attention away from your driving and increases your risk," spokesman Dylan Thomsen said.

"There's a reasonable difference between talking on your phone and to passengers who are in the same environment as the driver and more likely to realise what is going on. Passengers tend to mute their conversation."

As many people's phones doubled as music players, the AA's interpretation was that "infrequently" touching a phone attached to a car stereo to change a song would not be breaking the law, any more than changing the radio station would be, Thomsen said.

Ministry of Transport figures from 2014 showed distracted drivers were a factor in 12 per cent of crashes.

Distracted driving killed 22 people, seriously injured 191, and chalked up an estimated $297 million in social costs.

Between 2011-13, 163 fatal or injury crashes were attributed to drivers using cellphones.

Backing up the NZ data, a new report out of the US has suggested that smartphones and other driving distractions could be making roads there more dangerous.

Preliminary stats released Thursday (NZ time) showed US road deaths for January-June 2015 had risen 8.1 per cent to 16,225 which is a rate more than double an increase in overall driving spawned by falling fuel prices and a growing economy.

"The increase in smartphones in our hands is so significant, there's no question that has to play some role. But we don't have enough information yet to determine how big a role," said Mark Rosekind, who heads the National Highway Traffic Safety Administration, the US government's auto safety watchdog.

While US officials said it was too early to identify contributing factors. But Rosekind told reporters that officials are looking at likely causes including distracted driving and the possibility lower fuel prices have encouraged more driving among "risky drivers" such as teenagers.

Unlike NZ's laws, Rosekind also criticised an absence of effective laws in US states that prohibit hand-held smartphones by drivers or require the use of seatbelts and motorcycle helmets.

The New Zealand Transport Agency has even looked at independent research into hi-tech mobile phone detectors as it considered whether to nationally trial the devices in 2014.

They are designed to detect transmissions from passing drivers' phones and sort them from the background noise of other phones in the area.

The researchers concluded the detectors would be useful alongside visual observation – but there were concerns the detectors might pick up emails, calls and texts being received by a phone without the driver touching it.