Protesters gather in Paris ahead of labour law reform protests
Thousands of protesters are gathering in Paris after a demonstration over labour law reforms was authorised under a tense compromise between unions and the government.
Unions are holding a short march around the Bastille plaza to protest government plans to make working weeks longer and redundancies easier.
Similar protests against the legislation in recent months have degenerated into clashes between riot police and radicals.
Police threatened to ban Thursday's march, but the government agreed to let it proceed in a restricted area. Interior minister Bernard Cazeneuve warned that "no violence will be tolerated".
Police were systematically checking the bags of protesters before letting them enter the area.
Johanna Primevert, Paris police's spokeswoman, told BFM television that 18 people had been arrested, most of them for possession of objects that could be used as projectiles.
Authorities have ordered removal of some street furniture and protection of bus shelters to avoid potential damage. Some of the boats docked in a port between the Seine and the Bastille plaza have been moved on Wednesday.
Police have said some union members participated in and cheered recent violence. But the head of the influential CGT union, Philippe Martinez, insisted that the organisation is not an accomplice of the troublemakers and condemns them.
Other protests were organised for Thursday in France's major cities to oppose the government's labour legislation that is currently debated in the Senate.