The Shanghai Composite Index (SCI) closed at a three-week high Thursday after state-owned firms bought back shares of their listed subsidiaries, the Financial Times reported. The SCI ended the day up 3.6%, to close at 2,297.501. On Sunday, regulators moved to encourage state-owned firms to buy back shares to help prop up the market. That was in addition to other moves by regulators, such as the elimination of stamp duty, introduced after the SCI fell below 2,000 points last week. Thursday, authorities also reduced restrictions on stake purchases by shortening to 10 days, from 30 days, the ban on buying shares before the release of financial results.