PARIS - Violence broke out on Wednesday in a traditional May Day rally when labor unions, yellow vests and ultra activists took to the Parisian streets to denounce President Emmanuel Macron's policy and demand better work conditions.

TV footage showed police fired tear gas to push hooded individuals who had converged at the front of march, in Montparnasse Boulevard in Paris. They pelted anti-riot officers with stones and bottles and smashed a van's windows.

French Interior Minister Christophe Castaner warned on Tuesday of violence during May Day rally after far-left anarchist groups known as Black Blocs called on social media to make Paris "the capital of rioting".

Authorities said up to 2,000 radical activists from France and neighbor European countries would converge to the French capital to wreak havoc on the sidelines of union rallies.

According to Paris police headquarters, at least 165 people have been detained at 1100 GMT.

Earlier on Wednesday, police arrested three Spaniards suspected of planning violent acts. Police found in their bags materials that could be used as projectiles, including hammers and screwdrivers in addition to incendiary products, namely three gas cylinders and two cans of gasoline.

They also found a map detailing the route of the main unions' rally which is planned from Montparnasse train station to Place d'Italie metro station in southern Paris, about 2 km apart.

With orders from Macron to take an "extremely firm stance" against any kind of violence, more than 7,400 policemen were deployed across Paris, with identity checks and bag searches being reinforced, especially in sensitive sites including train stations.

Fearing violence and destruction of public properties, authorities have barricaded the neighborhood near the Elysee Palace, the National Assembly and Notre Dame Cathedral.

They also called on shops, restaurants and cafes located along the route of the rally to close by Wednesday afternoon, erect barricades and board up windows for fear of looting.