UPDATED 8.45am: A warning to drivers throughout Auckland and Northland on Christmas Eve as traffic is likely to be the worst it's been so far today.

Today marks the start of the busy period for holiday traffic throughout Auckland and Northland.

Data from previous years shows traffic will be very heavy heading north between Puhoi and Warkworth on State Highway One, and between Warkworth North and Whangarei, from today until January 2nd.

For those heading south from Whangarei to Auckland, the busy period is expected to last for longer from today until January 4th.

NZTA Highway Manager Brett Gliddon said this is one of the busiest times of the year, when people are heading away on holiday.

The agency is urging drivers to plan ahead to avoid delays and get to their destination safely - they are recommending drivers use the alternative route of State Highway 16 to spread traffic across the highway network.