DETROIT/TOKYO - General Motors regained its title as the world's top-selling automaker from Japanese rival Toyota in 2011 but the US company will have a challenge to stay on top after Toyota rebuilds its disaster-struck business.GM, bouncing back from bankruptcy less than three years ago, said on Thursday it sold more than nine million vehicles globally in 2011, up 7.6% from 2010, with its Chevrolet brand setting a sales record of 4.76-million vehicles.The Detroit-based automaker's return to the top slot comes after its 2009 taxpayer-funded bankruptcy restructuring allowed it to cut its spiralling legacy costs. It also comes as Toyota's sales fell an estimated 6% in 2011 to 7.9-million, thanks to severe production cuts following an earthquake, tsunami and nuclear crisis in Japan and killer floods in Thailand.TOYOTA REBUILDSThe Japanese automaker is ramping up production to rebuild depleted inventory and will add output capacity in emerging markets such as Brazil and China this year. But analysts said it also faced stiffer competition as rivals step up their game.JP Morgan auto analyst Kohei Takahashi said: "Toyota's biggest problem is that, even without the natural disasters, its sales weren't exactly growing."The ranking is not that important, but they need a convincing strategy to boost their sales," he said, adding that Toyota was behind rivals such as Nissan in rolling out small cars for emerging markets.Toyota's 2011 worldwide sales tally included listed subsidiaries Daihatsu and Hino Motors, and it put the carmaker just behind Volkswagen AG, which sold 8.16 million vehicles last year. Toyota is expected to publish a final sales tally for 2011 later this month.