PARIS (AFP) -- French President Francois Hollande on Wednesday threatened to ban demonstrations, the day after violent protests in Paris over labour reforms that the government vowed to push through regardless.

"At a time when France is hosting the Euro (football tournament), when it is faced with terrorism, demonstrations can no longer be authorised if property and people and public property cannot be safeguarded," Hollande's spokesman Stephane Le Foll told a cabinet meeting.

Earlier, a defiant Prime Minister Manuel Valls vowed to stand firm on the reforms despite the mass protests against them.

"The government will not change a text which is already the outcome of a compromise sealed several months ago with reform-minded unions," Manuel Valls told France Inter radio.

Hollande's Socialist government is trying to push through a set of reforms to the labour market in a bid to rein in down France's stubbornly high unemployment rate.

But critics see the reforms as skewed towards business interests, and strikes and clashes have flared in recent months.

On Tuesday, several hundred masked protesters hurled projectiles at police, who made dozens of arrests.

Forty people were hurt in the clashes, which came with France in the international spotlight as host of the Euro 2016 football championships.

Police said 29 members of the security forces were among those injured in Paris, while three cars were burned on the city streets.

Valls blasted the troublemakers, who he said wanted to "kill" the police officers patrolling the demonstration and accused the hardline CGT union, which organised the marches, of an "ambiguous attitude" towards those attacking the authorities.

"I call on the CGT not to organise this type of demonstration in Paris anymore," Valls said.

Two further protest days are set for later this month.

Police and organisers gave wildly different figures for the turnout, with unions saying 1.3 million people had turned out across France but police estimating the crowds at 125,000 or more, some 80,000 of them in Paris.