Prominent pro-democracy activist Nathan Law said Thursday he has left Hong Kong and will continue his campaign to warn against China's "authoritarian expansion" from abroad following Beijing's enactment of a controversial security law.Law's announcement on Twitter came a day after he testified before the U.S. Congress via videolink about the implications of the law, which has sparked an international outcry over its erosion of human rights and freedoms in Hong Kong. He did not disclose his current whereabouts.Related coverage:READ FULL ARTICLE