Public transport will be free in Auckland on Friday afternoon.

Auckland Transport said this morning that travel on all buses and trains would be free after 4pm on Friday.

Police said the Friday before Christmas was one of the worst days of the year for drink-driving.

AT group manager metro service delivery Stacey Van Der Putten said the organisation was working with police to reduce drink-driving and one key initiative was to provide free public transport on Friday so that people all across Auckland could have a drink after work and had no need to get behind the wheel at all.

"There's never been an excuse for drink-driving, it kills people on our roads. But if we can provide a free, easy public transport journey home, then it means there's no need to drive at all," she said.

Tamaki Makaurau road policing manager Inspector Scott Webb said police dealt with an increase in alcohol-related crashes during the festive season and urged people to plan how they would get home safely.

At 4pm the gates at train stations will be opened, and the tagging machines will be turned off on all bus trips starting after 4pm.

If your journey starts before 4pm but finishes after 4pm, this trip will not be free.