Authorities said 600 heavily armed police took part in an operation on Sunday to retake the 60km main road from Noumea to the airport that has been closed to commercial flights since the unrest erupted.
The local government estimates around 3,200 people are either stuck in New Caledonia or unable to return there from abroad since flights have been cancelled.
Australia and New Zealand have been pressing France for clearance to launch evacuation flights for their citizens.
Le Franc said about 60 roadblocks put up by pro-independence groups had been “broken through” without violence.
But the official added that the route was full of wrecks of cars, burned wood and metal which had only been cleared at 15 of the roadblocks. Le Franc said the road was also damaged in several places.
AFP journalists on the road found some roadblocks had been re-established by separatists, although they were eventually able to reach the airport.
Le Franc said police units would launch “harrassment operations” in coming hours to retake “hardcore” areas in Noumea and the towns of Dumbea and Paita.
“It is going to intensify in coming days” in zones held by independence activists, said Le Franc. “If they want to use their arms, they will be risking the worst.”
“I want to tell the rioters: Stop, return to calm, give up your arms,” added Le Franc, saying the crisis remained “unprecedented” and “grave”.
