Germany’s opposition leader has vowed to bar people from entering the country without proper papers and to step up deportations if he is elected as chancellor next month, as a knife attack by a rejected asylum-seeker spills over into an election campaign in which he is the front-runner.

Two people, including a 2-year-old boy, were killed and three others injured in a stabbing attack in Bavaria on Wednesday. The suspect, a former asylum-seeker who was supposed to be leaving Germany, was arrested.

Germany's main opposition leader demanded a sweeping overhaul of migration policy and permanent border controls on Thursday, a day after an Afghan asylum seeker was arrested for a deadly knife attack targeting children weeks before federal elections.