BRUSSELS—A car slammed at high speed into Carnival revelers in a small town in southern Belgium early Sunday, killing six people and leaving 10 more with life-threatening injuries, authorities said, adding many others were lightly injured. “What should have been a great party turned into a tragedy,” said Belgian Interior Minister Annelies Verlinden. The prosecutor’s office, which gave the death toll, also said two local people in their thirties were arrested at the scene in Strépy-Bracquegnies, 50 kilometers (30 miles) south of Brussels. Prosecutors said, in the early stages of their investigation, there were no elements to suspect a terror motive. In an age-old tradition, Carnival revelers had gathered at dawn, intending to pick up others at their homes along the way, to finally hold their famous festivity again after it was banned for the past two years due to the COVID-19 pandemic. Some dressed in colorful garb with bells …