At least 77 people have been detained across France during labour reform protests, which attracted an estimated 18,000 demonstrators in the French capital.

In Paris, demonstrators shouted anti-government slogans and sirens wailed in the background, as the march advanced on Thursday from the Bastille plaza through eastern part of the city.

Police fired tear gas at demonstrators and made several arrests of people accused of property damage.

Earlier, workers from all 19 nuclear power stations in the country voted to join employees from oil refineries and railways in the strike, which already shut down refineries and forced the government to tap into its strategic fuel reserves.

The strike have also led to rolling blackouts across the country.

The protesters are angry at a reform that gives employers more flexibility to hire and fire and weakens the power of unions.

The marchers said "there could be no compromise" until the government retracts the new labour law, Al Jazeera's Natacha Butler reported from Paris.

Similar protests were also held in major cities across France.

Manuel Valls, France's prime minister, denounced violence while speaking to the Senate, even as he hinted that there could be amendments to the law.

Valls' willingness to change the law signifies that the government knows that "the crisis is escalating and they want it to stop", Al Jazeera's Butler said.

"On all sides, the government really has suffered from this law," she said.

Pressure is rising on the government as queues at petrol stations lengthen by the day and with football fans due to flood into the country in two weeks for the Euro 2016 championships.

'Forced return'

As protests continued, the head of France's oil industry lobby said the government is considering forcing workers to return work if the stoppages drag on.

In an interview with AP news agency, Francis Duseux said on Thursday that the French government has used four days' worth of its strategic fuel reserves to compensate for oil shortages.

Duseux, of industry coordinating group UFIP, said only two of the country's eight refineries are working normally.

Duseux said about 20 percent of petrol stations were suffering shortages on Thursday, compared with 30 percent earlier in the week. Police have been sent to force open fuel depots blocked by strikers.

The country has nearly four months of fuel reserves and President Francois Hollande told a cabinet meeting that "everything will be done to ensure the French people and the economy are supplied".

Worried drivers were using online apps to find petrol stations that still had fuel, with many limiting drivers to only 20 litres each.