French farmers were on Tuesday maintaining roadblocks on key highways into Paris for a second day, increasing pressure on the government for more concessions in an intensifying standoff.

Prime Minister Gabriel Attal is expected to address parliament and announce new measures aimed at assuaging the anger of farmers over their working conditions, as he faces his biggest crisis since being named by President Emmanuel Macron this month.

The farmers have now staged over a week of protests, which have spread to the capital where tractors, hay bales and other objects have since Monday prevented motorists from entering the Paris along several key routes.

The government has so far promoted a softly-softly approach with the protesters, while making clear that any attempts to block Paris's main airports or the vast Rungis wholesale food market to the south of the city would be a red line.

A police source told AFP that around 1,000 farmers and 500 vehicles had been involved in Monday's actions and they appeared intent on keeping up the protest until Friday.

A convoy of producers who left on Tuesday morning from the southwestern town of Limoges heading for Rungis changed route after being blocked by gendarmes, organisers said.

Armoured vehicles of the gendarmerie have been deployed around Rungis to ensure food supplies are not disrupted.

Farmers were however seeking to block roads heading to the airport of the southwestern city of Toulouse, which is surrounded by agricultural regions.

Meanwhile, farmers spent the night in tractors on key routes heading to the capital.

"The night was short, we'll have to bounce back but we're up for it", said Samuel Vandaele of the FDSEA farmers' union for the Paris region, under a motorway bridge some 30 kilometres outside of Paris.

But he added: "We all want to return to our farms and our animals."

Attal is due to announce new measures in a speech to parliament, after the main farmers union judged that a first battery of measures announced on Friday did not go far enough.

"The watchword is to stay as long as we do not have an answer to the main issues", Thomas Robin, a cereals farmer producer and also of the FDSEA, told AFP.

French farmers are angry about incomes, red tape and environmental policies they say undermine their ability to compete with other countries and have left France increasingly dependent on imports.

Ecologists however fear more concessions from the government could undermine its environmental pledges.