Police and the New South Wales Workcover Authority have un-covered a one and a half tonne illegal fireworks cache at a property north of Mittagong.

Acting on a tip off from the public investigators went to a location at Wilton near Picton and found pyrotechnics, explosives and detonator cord.

Workcover says the haul included large mortars, sky rockets, and bungers, all of which have been illegal in New South Wales for decades.

The haul has been taken away for destruction.

No charges have been laid at this stage,  but police warn the illegal possession of fireworks carries up to 12 months jail and a fine of up to $27,000.