Thousands of protesters clashed with police in central Paris and other French cities on Thursday, as union activists around the country stepped up industrial action over a raft of labor reforms.

Between 18,000 and 100,000 people joined the march in the French capital before it took a violent turn in the afternoon. Masked individuals reportedly smashed the windows of high street shops and banks as police fired tear gas on the crowd. Sixteen people were arrested. There were similar scenes in the western city of Nantes, while in southwestern Bordeaux around 100 people stormed a police station.

Protesters demand the government abandon a controversial labor reform bill that makes it easier for employers to hire and fire workers, and relaxes rules around the 35-hour work week.

The government forced the bill through parliament earlier this month. It says the legislation will create jobs and tackle unemployment, which hovers at around 10 percent. Union representatives have said they see the reform as a tool to erode workers' rights.

Wave of industrial action

Union anger over the changes has led to strikes across France that have affected oil refineries, fuel depots, ports, train services and some flights. The wave of industrial action has had a particularly disruptive impact on fuel supply, resulting in days of shortages at gas stations.

In the port city of Le Havre on Thursday, dock workers set off smoke bombs and fireworks in front of the city hall. Dock workers also went on strike in the southern port city of Marseille, preventing ships from offloading oil and gas.

Francis Duseux, the head of France's oil industry lobby, said the government had been forced to dip into four days' worth of its strategic fuel reserves for the first time in six years to compensate for the resulting supply problems. He said only two of the country's eight refineries were working normally.

More protests ahead

Another round of protests is planned for June 14, four days after the 2016 European Championships soccer tournament kicks off in France.

Members of the CGT union, one of the seven unions that called for the nationwide strike, warned the tournament could face major disruptions if the government refuses to scrap the bill.

French Prime Minister Manuel Valls said abandoning the reforms was not an option, but he did open the door to possible "improvements and modifications" to the legislation.

"I am always open when some aspect should be improved, but on the main lines of the text, particularly Article 2, there is no question of touching it," said Valls on broadcaster BFM-TV. "We cannot cede to a desire to make the government fold by blocking the economy."

Under Article 2, companies can opt out of national labor protection obligations if they adopt in-house deals on pay and conditions with the consent of employees. CGT union members have rejected the offer, and say they will continue striking until the bill is dropped.

nm/sms (Reuters, AFP, AP, dpa)