French police intervened to clear demonstrators from a central Paris square Thursday where a crowd of thousands had gathered in front of parliament to protest President Emmanuel Macron's pensions reform.

Lines of police with shields and batons drawn advanced towards the square, while others fired water cannon after a fire was lit in the middle of the square.

The government Thursday invoked a special constitutional power to enact a contentious pension bill without a vote in parliament, in a risky move announced by Prime Minister Elisabeth Borne.

The decision was made just a few minutes before the vote was scheduled because the government had no guarantee that the bill would command a majority at the National Assembly, France’s lower house of parliament.

The bill will raise the retirement age from 62 to 64, and is the flagship legislation of President Emmanuel Macron's second term. The unpopular plan has prompted major strikes and protests across the country since January.

The move is expected to trigger a quick no-confidence motion in Macron's government. The Senate adopted the legislation to raise the retirement age to 64 on Thursday morning, but a ballot in the lower house National Assembly scheduled for the afternoon was seen as extremely tight.

Trains, schools, public services and ports have been affected by strikes over the last six weeks, while some of the biggest protests in decades have taken place. An estimated 1.28 million people hit the streets on March 7.

A rolling strike by municipal garbage collectors in Paris has seen around 7,000 tonnes of uncollected trash pile up in the streets, attracting rats and dismaying tourists. The strike has been extended until next Monday, with the prospect of serious public health problems leading to growing calls for authorities to intervene.

City police chief Laurent Nunez informed mayor Anne Hidalgo on Wednesday evening that the government would use its power to "requisition" workers, meaning some of them will be forced back to work under threat of prosecution.

Hidalgo has defended the protests as "fair", although her office has contracted private refuse companies to clear trash in some areas, including in front of schools and creches.