(ANSA-AFP) - BELGRADE, 01 MAG - Serbia's trade unions joined thousands of protesters in a May Day rally called by student leaders Thursday, six months after a deadly train station tragedy that sparked mass demonstrations against corruption. Thousands gathered in the capital Belgrade and the northern city of Novi Sad, where the collapse of a renovated railway station last November killed 16 people in a tragedy widely blamed on corruption and poor oversight. Thursday's rallies on international Labour Day were the latest in a wave of unrest sparked by the disaster, which led to the resignation of a prime minister and the fall of the government. Whistling, crowds of all ages converged in the early afternoon in front of the government building in Belgrade, some waving red, white and blue Serbian flags and others the colours of their unions. The students announced on their official Instagram account ahead of the rallies that their "struggle is entering a new phase". Zeljko Veselinovic, leader of the "Sloga" (Unity) union, stressed the importance of the development. "The students have united us," he told AFP. "In my 20 years of union work, it has never happened that these five unions stood together at a protest -- or even in the same room -- working on something jointly," he added. Earlier on Thursday, thousands of people gathered at the train station in Novi Sad, six months to the day since the disaster, Beta news agency reported. They held red heart-shaped balloons bearing the names of victims and unveiled a plaque commemorating those killed. (ANSA-AFP).