Alex Armstrong has launched a scathing attack on footage showing French police slashing a migrant boat, dismissing the intervention as "complete political theatre".

The incident that sparked Armstrong's criticism occurred early Friday morning on a beach south of Boulogne.

French police officers waded into shallow waters and used knives to slash an inflatable boat packed with men, women and children.

The vessel was wallowing dangerously in the waves when officers intervened. All passengers managed to clamber to safety as the boat collapsed and rapidly deflated.