Darkness had just fallen on the Bahrain international circuit when the air was shaken by a rapid series of explosions. It was a false alarm – officials had chosen this hour to launch a firework display to celebrate the opening of a new go-kart track by the main circuit – but the horrified expressions on the faces of motor racing teams on the first of three "days of rage" called to coincide with Sunday's Bahrain grand prix spoke volumes.

On the north side of the island, an estimated 50,000 pro-democracy demonstrators had gathered. Here the explosions came from tear gas rounds and guns as police fired at protesters to try to disperse them.

"It's terrible up here," one eyewitness said. "The police are using a combination of tear gas and pepper spray. There are also rubber bullets. The crowd is huge, tens of thousands. It seems there will be lots of trouble tonight. There is going to be a big protest in Manama, the capital, and also in the villages."

One of the country's leading activists said: "Thousands of us were on the Budaya Highway trying to get back to the track but we were driven back by the police using teargas."

Another protester said: "The big group was broken down into several smaller groups. And the police were very heavy-handed as soon as they knew there was no media around. A lot of protesters were beaten."

Ala'a Shehabi, one of the country's most prominent protesters, claimed last night: "Abdulhadi Alkhawaja [the hunger striker] has called his lawyer to ask him to come and take his will as he prepares for death. It seems the government are hell bent on letting him die than releasing him."

At the circuit's media centre, pictures started circulating among the gathered journalists of protesters on the highway running north being attacked by police. Out in the paddock, meanwhile, the mood was sullen, with members of the 12 Formula One teams unhappy that the race will take place against a background of violence and oppression.

The Force India team left first, refusing to take any part in the second practice session in the afternoon after four of the team were involved in a petrol bomb incident on Wednesday night.

Beside them in the paddock is the Sauber team, who reported that a number of the personnel had been confronted by masked protesters on Thursday evening.

Another team reported that a protester had entered their hotel and screamed: "Do you know that by being here you have killed 80 people!"

If this weren't enough to unsettle them, the hackers' collective Anonymous on Friday announced its own attack on the grand prix: "We have watched this tyrannical government teargas its own people literally to death, with over 30 fatalities so far.

"We have watched as thousands of innocent protesters and activists have been jailed," the organisation said in a statement.

"The king of Bahrain be warned, we are about to unleash the worst shitstorm you have ever seen – and your time as dictator is over."

Anonymous added a personal message to Bernie Ecclestone, the sport's commercial rights holder: "Anonymous will turn your web site into a smoking crater in cyber space.

"We will also jam your phone lines, bomb your email inboxes – and wreck anything else of yours we can find on the internet."

Formula One's renowned bubble was putting on a bullish face against the onslaught. Ecclestone, who recently described Bahrain as "quiet and peaceful", told journalists that he couldn't call off the race.

"It's nothing to do with us," he said, shrugging. "The national sporting authority in this country can ask the FIA if they want to call the race off.

"You guys love it," he said to the throng of journalists. "What we really need is an earthquake or something like that, so you can write about that now.

"I think you guys want a story and it is a good story. And if there isn't a story you make it up as usual. So nothing changes."

The crown prince of Bahrain, Sheikh Salman bin Hamad Al-Khalifa, standing alongside Ecclestone, said: "I hope by coming here you understand that unlike what has been reported, we are not trying to say we are perfect. We are a real country with real issues.

"I hope you get a chance to see us for all our complexities, all our shades."

Jean Todt, president of the FIA, the sport's ruling body, was also at the paddock on Friday, though he said nothing. His son, Nicolas, shares ownership of the Lotus ART GP2 team with the crown prince.

Meanwhile team principals looked like stooges when asked to justify their presence in this unhappy land.

Martin Whitmarsh, of McLaren, said: "Ultimately we're a race team. We're here to go motor racing and that's our number one priority."

Norbert Haug of Mercedes nodded: "Absolutely the same."

Christian Horner, of Red Bull, said: "Martin's summed it up perfectly, I think. Formula One is a sport at the end of the day and it's wrong for it to be used politically."

Some might argue that is exactly what the Bahrain government is doing with their "uniF1ed" posters.