The New Zealand Transport Agency is warning of the potential for "significant delays" on the State Highway 2 stretch between the Hawke's Bay Showgrounds and Farndon Park in Clive this afternoon as the Water Conservation Order rally is staged.
An NZTA spokesman said motorists were advised to use alternative routes from midday to mid-afternoon.
The rally will see a string of vehicles including tractors and agricultural machines setting out from the showgrounds at 12.30pm for the rally venue in Clive, where events are set to get under way at 1.15pm.
People who set out to travel along that stretch at that time can expect to add about 10 minutes to their journey.
Motorists travelling SH2 south between Hastings and Takapau won't have their travel times affected but they are being advised to drive with caution along some sections as roadmarking work is being carried out this week and heavy vehicles will be operating.