Quitline was inundated yesterday with calls from smokers seeking a fresh start to the new year.
Spokesman Bruce Bassett said more than 400 smokers had been in contact.
About 200 people had called into the service and a similar number had been in touch via email and blog, he said. And the online messages were still coming in.
"Clearly New Year's resolutions and the [tobacco] tax increase are the things that motivate people to change," Mr Bassett said.
"It's a very, very busy day."
Mr Bassett said the organisation employed extra staff to cope over the holiday period, which is their busiest time of the year.
On a normal Tuesday, Quitline would probably receive only a third of the calls, messages and sign-ups received yesterday, he said.
Staff are bracing themselves for tomorrow - the first official day back at work after the New Year's period. That is the busiest day they experience, Mr Bassett said.
Between 8000 and 10,000 people are expected to contact Quitline this month.
Last year, 8222 people signed up to Quitline in January, compared with 9383 in January 2011.
In 2010, only 4966 registered throughout January. Quitline communications manager Jane MacPherson said the increase between 2010 and 2011 was likely because of the tobacco tax hikes.
"There was no tax increase in 2010."
Yesterday also marked the first of four annual tobacco tax increases. Each year the tax will rise by 10 per cent.
Treasury previously said the hikes would result in a packet of 20 cigarettes costing about $20 by 2016.
Figures show about one in five Quitline clients are successful after 12 months.
At six months, the quit rate is 24.2 per cent.
"That tells us it's a really low rate of relapse between six and 12 months," Ms MacPherson said.
About 62,500 people signed up with the Quitline service last year, Ms MacPherson said, with 15,000 of them still smoke-free.
* 17 per cent of NZ adults are smokers
* Down from 21 per cent in 2006 and 33 per cent in 1983
* 11.1 per cent excise increase today
* $16: average price of pack of 20
Who can help?
* Quitline - 0800 778 778.