Bahraini security forces have clashed with protesters against Bahrain's controversial Grand Prix in mainly Shia villages despite increasing security for the start of practice sessions.
The overnight clashes between protesters and security forces across Shia villages continued into the early morning on Friday, witnesses said.
Formula One cars took to the track in Bahrain at about 07:00 GMT, with the government hoping for a successful Grand Prix, while activists are promising to mark it with "days of rage" after more than a year of Arab Spring protests.
"The people want to topple the regime," chanted dozens of protesters carrying pictures of jailed hunger striker Abdulhadi al-Khawaja. "Down Hamad," they called, referring to Bahrain's king, Hamad bin Isa Al Khalifa.
Met by tear gas and sound bombs, the protesters responded by hurling petrol bombs at security forces, witnesses said.
Security forces also fired buckshot to disperse the crowds, wounding dozens of people.
Protesters burned tyres, briefly blocking several main roads leading to the Sakhir circuit where Friday's Formula One practices were taking place, witnesses said.
Al Jazeera's correspondent in the capital Manama, who we are not naming due to reporting restrictions imposed by Bahrain's government, said a protest by anti-government demonstrators "will be held later today on the main highway in capital, where they will come out in force to show the world that Formula One really is not welcome here".
He said many were plagued with "security concerns".
"Most tourists and Formula One spectators are choosing to stay away from this race because it is just too controversial for them, I think people feel their security and personal wellbeing, cannot be guaranteed enough to make the trip worthwhile."
'Days of rage'
The February 14 Youth Movement had called on social networking sites for "three days of rage" to coincide with the event.
And Bahrain's main opposition group, Al-Wefaq, called for a week of daily protests to coincide with the Grand Prix, to focus media attention on their longstanding demands for greater equality in the Sunni-ruled kingdom.
The government has barred the opposition from holding protests in Manama itself.
Earlier this week, hundreds of protesters marched carrying banners held a demonstration near Bahrain's international airport as the race teams flew in, despite the arrest of about 80 leading pro-democracy activists.
"A number of rioters and vandals had been arrested for taking part in illegal rallies and gatherings, blocking roads and endangering people's lives by attacking them with petrol bombs, iron rods and stones," the Information Affairs Authority
said in a statement on Friday, citing Major-General Tariq Al Hassan.
However, activists accused Bahrain's's rulers of using the race to improve their international image.
"Formula One in Bahrain has been taken as PR for the ruling elite, the repressive dictators who are ruling the country,"
Nabeel Rajab, an activist, said.
Mohammed Al-Maskati, president of Bahrain Youth Society for Human Rights, told Al Jazeera the mood in Manama in the run-up to Sunday's race was one of "anger".
He said the protesters "are very angry that [the] Formula One [race] was not cancelled - they want to send a message to say that sports must not support dictatorships and human rights violations".
Two members of the British-based Force India team, travelling between Bahrain International Circuit and their hotel
in Manama, were asked to go home after seeing burning petrol bombs in what the government described as an isolated incident.
The Bahrain Grand Prix was cancelled last year in the wake of large-scale anti-government protests and a crackdown that followed in which a government commission said 35 people were killed.
While sports correspondents poured into Bahrain this week to cover the race, non-sports reporters from some other news organisations have not been granted visas to visit the country.