Arrests since the Myanmar coup were approaching 500 as the junta pressed on with attempts to stymie nationwide opposition by blocking the internet and sending troops. For a second day, some motorists in Yangon blocked roads with vehicles, leaving their bonnets up and pretending they were broken down to stop security forces from moving around Myanmar's biggest city. Buses and cars were parked around a bridge at North Dagon on Thursday morning, as protesters chanted: "Don't attend the office, leave it. Join the civil disobedience movement." "We gathered about five taxies and one pretended his car had broken down and blocked the street. Others also surrounded him. But we didn't stay long. We blocked [for] about 30 minutes," said a 30-year-old taxi driver. "We are doing this to cause difficulties for police. If they come and it's a little bit tense, we leave then." Than Than, 50, a street food vendor, said the traffic jams were inconvenient, but she supported the campaign. "I walked about 40 minutes because of cars blocking my way back home yesterday afternoon before I got a bus," she said. Tensions flared overnight in Myanmar's second-biggest city Mandalay, when police and soldiers broke up a protest that blocked the railway. A member of a local emergency rescue service said security forces opened fire, although it was not clear whether rubber bullets or live rounds were used. One person was injured. Four train drivers participating in the civil disobedience movement were arrested at gunpoint, taken to a Mandalay locomotive factory and forced to drive to the northern city of Myitkyina, the Assistance Association for Political Prisoners said. Myanmar's civil disobedience movement is having a clear effect on official business. Despite junta appeals for civil servants to return to work and threats of action if they do not, there has been no sign of the strikes easing. The junta issued arrest warrants against six celebrities for encouraging the strikes. The charges can carry a two-year prison sentence. Some of those on the list were defiant. "It's amazing to see the unity of our people. People's power must return to the people," actor Lu Min said. Meanwhile, hackers attacked Myanmar government websites on Thursday to protest against the military coup. A group called Myanmar Hackers disrupted websites including the central bank, the military's propaganda page, state-run broadcaster MRTV, the port authority and the food and drug administration. "We are fighting for justice in Myanmar," the group said. Internet access was severely curtailed for the fourth consecutive night at about 1am on Thursday, according to NetBlocks, a group that monitors internet closures around the world. It said connectivity dropped to 21 per cent of ordinary levels and was restored eight hours later before the start of the working day. "The practice is detrimental to public safety and incites confusion, fear and distress in difficult times," NetBlocks tweeted.