Gunfire erupted in the centre of the capital when armed members of a pro-government vigilante group arrived on motorcycles and began firing at more than 100 anti-Maduro student protesters clashing with security forces At least four people have been killed, including a police officer, after thousands of Venezuelans opposing President Nicolas Maduro took to the streets of Caracas following two weeks of anti-government protests across the country. Wednesday's protest, organised by students and hardline opposition members, was the biggest faced by Maduro since he was elected nearly a year ago following the death of his mentor, Hugo Chavez. Al Jazeera's Girish Gupta reports from Caracas.