Road traffic near the northern French port of Calais was back to normal Tuesday after hundreds of migrants tried to block a major road and board trucks stuck in the traffic jam, drawing police intervention and clashes between the migrants and law enforcement.

The clashes took place near the Camp de Lande — a sprawling migrant camp on the outskirts of the city home to at least 3000 people.

Authorities reported that migrants threw rocks, mattresses and branches onto the road to bring traffic to a standstill in an attempt to board vehicles to Britain. According to local daily La Voix du Nord, riot police officers used up more than 600 canisters of tear gas to disperse the migrants. The prefecture told VICE News that the clashes lasted until around 5pm, and that it took officials another two hours to clean up the road and for traffic to resume.

A spokesperson for the Pas-de-Calais prefecture said that between 200 and 300 migrants started obstructing the road around 3:00pm. According to the spokesperson, migrants took advantage of the heavy traffic caused by UK returning from the 2016 Euro soccer tournament and the 24 Hours of Le Mans car race.

No police officers or migrants were injured during the clashes. Police made three arrests Monday, including one Syrian migrant who was throwing projectiles at officers.

Two British activists were also arrested, one of them for vandalizing an official vehicle, the other for opposing his colleague's arrest.

The prefecture said that an extra 560 police officers have been mobilized to secure the area — eight teams of 70 officers who carry out round-the-clock patrols.

The British government has also funded additional fencing to secure the road leading to the port. Construction on the fence started in May, and is expected to be complete in July. In its article on Monday's clashes, La Voix du Nord reported that some migrants were able to break through the fence using crowbars.

Migrants regularly die in Calais attempting to reach Britain through the Eurotunnel or trying to board UK-bound vehicles that cross the English Channel on ferries. Generally, attempts to storm UK-bound vehicles happen under the cover of night, and the prefecture said that officers were now equipped with infrared goggles to spot migrants in the dark.