Tens of thousands of anti-government protesters blocked a major road in Bahrain ahead of Sunday's F1 Grand Prix in the Gulf kingdom.
Some in the crowd carried banners with the slogan: "Don't race on our blood."
The rally along Budaiya Highway followed a night of heavy clashes between demonstrators and security forces.
Activists have demanded that F1 bosses cancel the race due to Bahrain's poor human rights record.
The race, which was first run in Bahrain in 2004, was cancelled two years ago following the forced clearance of a Manama landmark, Pearl Roundabout.
In the unrest that followed more than 50 people died, hundreds were arrested and thousands dismissed from their jobs.
Last year's race went ahead in an atmosphere of heightened security. One protester was shot dead by police.
But in a joint statement on Friday, motorsport's world governing body and Formula One management said this year's race should proceed as planned.
The Federation Internationale de l'Automobile (FIA) and Formula One Management (FOM) said they "also strongly believe sport can often be a force for good and that the staging of the Grand Prix in Bahrain will come some way in helping soothe some of the issues which have been raised in the media".
Crown Prince Salman bin Hamad bin Isa al-Khalifa told the BBC's Dan Roan the event would be safe for teams and spectators.
He added: "I'm sure that after the demonstration, which is legal and licensed and has gone through all the proper procedures, there'll be a very small minority of violent protesters who will try to cause some trouble with the police.
"But that's par for the course, unfortunately."
Protests were reported across the kingdom on Thursday night, with demonstrators chanting "No Formula on Bahrain's occupied land", according to AFP news agency.
Protesters blocked roads with burning tyres, and police responded with tear gas and stun grenades.
The Bahrain Center for Human Rights says 13 people were arrested on Thursday and that there had been clashes in villages close to the Sakhir track, the site of the race, south of the capital, Manama.
A centre spokesperson said police had fired tear gas and birdshot against protesters in the towns of Sitra and Diraz.
The authorities are anxious for Sunday's race to pass off without incident, and checkpoints have been set up at junctions leading to the track, AFP reports.
F1 practice sessions were held at the circuit on Friday, ahead of qualifying rounds on Saturday.
The main opposition society Al-Wefaq says more than 100 people have been arrested this month, many from the villages near the circuit.
The organisation appealed for massive peaceful protests on Friday, but it has not called for the race to be cancelled.
For the past two years members of the Shia majority have been protesting against alleged human rights abuses by the ruling Sunni minority.
The latest clashes come after days of escalating tensions.
On Tuesday, police fired tear gas and clashed with students in a raid on a secondary school in the capital, Manama.
Officers stormed the Jabreya school for boys after students staged a protest demanding the release of a colleague arrested on Monday, activists say.
On Sunday a car bomb blew up in the heart of the financial district in Manama, though without causing injuries.