BEIJING (Reuters) - The death toll from Beijing's heaviest rainstorm in six decades more than doubled to 77 after rescuers found more bodies, the official Xinhua news agency said on Thursday, citing the city's municipal government.

Saturday's storm flooded roads, sent torrents of water tumbling down steps into underpasses and drowned a number of drivers trapped in flooded streets.

Many residents took to China's popular microblogging sites to criticize the poorly managed drainage system in the Chinese capital that boasts modern highways and skyscrapers.

Some posted pictures apparently showing the capital's historic Forbidden City area emerging from the floods unscathed - thanks to its efficient drainage systems built about 600 years ago.

The municipal government put the cost of the damage at around 12 billion yuan ($1.88 billion), according to state media.

Rescuers had been trying to retrieve bodies from wreckage and rivers in the capital's worst-hit southwestern area of Fangshan, the agency added. The initial estimate of the death count was 37.

(Reporting by Kevin Yao; Editing by Andrew Heavens)