Clashes broke out in the latest "yellow vest" protests in French cities Saturday but a massive police deployment prevented more of the rioting and looting that marred last week's rally in Paris.

More than 40,000 people took to the streets across France for a 19th consecutive week of anti-government protests -- 5,000 of them in the capital -- Interior Minister Christophe Castaner said.

Most of the "yellow vest" protests were relatively calm but scuffles broke out in Paris in the afternoon as police moved in with tear gas against a hard core of hooded demonstrators, many wearing gas masks or helmets.

A 75-year-old woman was seriously injured in the southern city of Nice when she fell and hit her head during a police charge.

Authorities had vowed zero tolerance of any violence, outlawing the protests in a large area of western Paris for the first time.

That included the Champs-Elysees, the scene of last Saturday's rampage by hundreds of black-clad agitators.

This time around 6,000 security forces backed by armoured vehicles and water cannon were mobilised in the capital, where a march ended at the Sacre-Coeur basilica with few incidents.

Police later blocked off a boulevard where dozens of protesters set fire to garbage bins before fleeing toward the Place de la Republique, where they gradually dispersed.

One officer suffered a heart attack at the scene and was taken to hospital in serious condition, a police source told AFP.

The government said 32,000 people joined in the demos last weekend nationwide with 10,000 in Paris.

This time at least 70 people were detained in the capital, while around 50 were given fines -- which the government hiked by decree this week to 135 euros ($153) from 38 euros -- for protesting in the outlawed sectors, the police said.

Protest bans were also in effect in the centres of Toulouse, Bordeaux, Dijon, Rennes and the southern city of Nice, where Chinese President Xi Jinping is to meet his French counterpart Emmanuel Macron this weekend.

Dozens of people who defied the ban at Nice's Garibaldi square near the port were quickly surrounded by security forces and later evacuated, with 75 people arrested.

Clashes also broke out in other cities including Bordeaux, Nantes and Montpellier.

"The movement has to continue, we owe it to the injured," said Martine, a 66-year-old pensioner in Toulouse, referring to the hundreds of people hurt since the protests began four months ago.

"The much-touted social ladder is broken. We're all workers or low-paid employees, we're not making it," she said.

- Bringing in the army -

President Emmanuel Macron was under pressure to avoid a repeat of last week's rioting on the Champs-Elysees, where over 100 shops were damaged, looted or set alight.

His government drew fierce criticism over its handling of the protests, when police appeared to hang back during the wave of rioting and vandalism that swept the iconic avenue.

The Paris police chief was fired just a few days later, and his replacement Didier Lallement warned Saturday that his officers would move to "immediately end any violence or destruction."

On Saturday "our instructions for firmness... enabled order to be maintained and prevented things getting out of hand," Castaner said.

The government also redeployed soldiers from its Sentinelle anti-terror force to guard public buildings Saturday, freeing up police to tackle the flare-ups of violence.

There was no sign of the soldiers in much of central Paris on Saturday, but the move drew fierce criticism from opposition parties, who have accused the government of playing with fire.

On social media, several "yellow vest" leaders had urged caution, warning demonstrators against appearing to support the violence by far-left or far-right infiltrators.

- 'Financially beaten' -

The demonstrations began last November over fuel tax increases and spread into a full-scale protest against Macron, accused of favouring the rich at the expense of rural and small-town France.

The centrist president is also accused of being out-of-touch with the struggles of many voters.

Pictures of him skiing last weekend before rushing back to Paris for a crisis meeting over the violence drew widespread scorn on social media.

He has loosened the state's purse strings to the tune of 10 billion euros ($11.2 billion) to try to defuse the rallies with a package of financial relief for low-earners.

He also embarked on a three-month "great national debate" with a pledge for more participative democracy, but he has refused to back down on his decision to abolish a wealth tax -- a key source of protesters' ire.

In a Facebook video this week, Maxime Nicolle, one of the protest movement's figureheads, said the rioting in Paris and other cities was the result of "40 years of being beaten psychologically and financially" by successive governments.