THE AFL's heat policy will be invoked for Saturday's NAB Challenge games, with blazing conditions forecast for Essendon's clash with Geelong in Shepparton and North Melbourne's hit-out against Collingwood in Wagga Wagga.

Quarters will be reduced to 22 minutes for both matches and end-of-quarter breaks will be extended.

Players in both games will now have eight-minute breaks at quarter and three-quarter time and 25 minutes at half-time.

The Bombers take on the Cats in Shepparton at 2.05pm (AEDT), with the mercury expected to hit 37 degrees with only light winds forecast by the Bureau of Meteorology.

North Melbourne and the Pies kick off later in the day at 4.40pm (AEDT) with temperatures likely to reach 38 degrees.

All teams are still allowed to have eight players on the interchange bench this weekend.

A decision about enacting the heat policy for Sunday's games between the Western Bulldogs and Melbourne in Craigieburn and the Brisbane Lions and St Kilda in Mackay will be made on Saturday.