Belgian federal police used heat-tracing technology to clamp down on fans watching Sunday's action at Spa-Francorchamps from nearby wooded areas.

The news comes just a day after police turned away from the track a full bus-load of Max Verstappen fans from Holland.

The Dutch publication Formule 1 reports that Belgian police even released heat-seeking images taken from a helicopter depicting fans in nearby forests.

"Some attempts to gain access to the circuit were thwarted thanks to the technological means deployed," the Belgian federal police confirmed.

"Thank you to those fans who respected this closed event."