China\'s security chief has told provincial officials they need to be more prepared for the \"negative impact\" of slowing growth, underscoring Beijing\'s concern a slowdown could bring social unrest. Large-scale strikes have swept China\'s southern manufacturing heartland in recent weeks, as workers face off with employers juggling high costs and exports shrunk by lower demand from the debt-burdened West. Zhou Yongkang, a member of the Politburo, said in a speech to officials from north China Friday that authorities needed to improve their system of \"social management\" -- including increasing \"community-level\" manpower. \"In the face of the negative impact of the market economy, we have not formed a complete system of social management,\" Zhou said, in comments reported by the state Xinhua news agency at the weekend. \"It is urgent that we build a social management system with Chinese characteristics to match our socialist market economy.\" China\'s economy grew by 9.1 percent in the third quarter, down from 9.5 percent in the previous quarter, while manufacturing -- a key driver of growth -- slumped to its lowest level in nearly three years last month. Details and images of many of the recent strikes have emerged first via Twitter-like social networking sites called weibos that Chinese authorities are struggling to purge of what officials call \"rumours\" and \"false news.\" More than 7,000 workers walked off the job in south China\'s Guangdong province last month, shutting a factory making New Balance, Adidas and Nike shoes and clashing with police in a protest over layoffs and wage cuts.