French truckers began blocking motorways and fuel depots on Monday at the start of a series of demonstrations against President Emmanuel Macron and changes to labour law.

Drivers from the CGT and FO trade unions moved into position before dawn on a motorway near the northeastern border with Belgium while others blockaded roads near major cities such as Marseille and Bordeaux.

Macron has faced two days of strikes and demonstrations from the CGT in the last fortnight and a protest rally by the hard-left France Unbowed party at the weekend, but has vowed to press on with the changes.

"It's not by blocking the French economy that will make it better," junior economy minister Benjamin Griveaux told RTL radio on Monday, adding that the government would continue to talk with truckers' unions.

The government has said that the country has sufficient petrol and diesel stocks to ride out the blockade -- which might be extended later in the day -- but has warned that panic buying by drivers would increase the risk of major disruption.

The labour market reforms, signed by Macron last Friday, are designed to give employers more flexibility to negotiate pay and conditions with their workers while making it easier and less costly to shed staff.