Tens of thousands of anti-government demonstrators have begun marching in Seoul in what police say could be the largest protest at the South Korean capital in nearly a decade.

A Seoul police official said Saturday about 80,000 people are expected to turn up in the downtown rallies.

The marches, organized by an umbrella labor union and civic groups, bring together protesters with a diverse set of grievances against the government of conservative President Park Geun-hye, including her business-friendly labor policies and decision to require middle and high schools to use only state-issued history textbooks in classes from 2017.

Critics say that books, which haven't been written yet, would be politically-driven and might attempt to whitewash the brutal dictatorships that preceded South Korea's bloody transition toward democracy in the 1980s.