Pro-separatist groups have clashed with police over the trial of 12 Catalan separatist leaders on Thursday.

The protests have been disruptive. Riot police used batons on a group of young protesters in downtown Barcelona. At the Plaza Catalunya station, demonstrators occupied the rail tracks to stop train traffic.

Demonstrators blocked major roads with rallies and burning tires. According to authorities, around 20 roads were cut off, including the A7, which links Spain to France and the A2 which runs between Madrid and Barcelona. A police spokeperson said some of these blocks have since been removed.

One resident posted a video showing a large column of smoke rising over burning tires on a highway.

The protests began as a general strike, called by students and small unions of pro-independence workers.

But although intended as a demonstration for labor law reforms, crowds carried pro-secession flags and chanted for the release of the separatist leaders on trial.

The general one-day strike has brought parts of the region to a standstill

Catalonia declared its independence from Spain in 2017, after holding a referendum outlawed by Spain's Supreme Court.

Twelve leaders of this separatist movement were arrested later that year, nine of whom have since been held without bail, awaiting trial.

They could be jailed for up to 25 years, on charges of rebellion, sedition and misuse of public funds.

Read more: Catalonia crisis: Spain takes over regional parliament, calls elections after independence declaration

nn/msh (Reuters, AP)