SEOUL: Police used tear gas and water cannons Saturday as they clashed with anti-government demonstrators who marched through Seoul in what was believed to be the largest protest in South Korea's capital in more than seven years.

About 80,000 people were expected to turn up for the downtown rallies that were to stretch into the evening, according to an official at the Seoul Metropolitan Police Agency, who didn't want to be named, citing office rules.

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

Demonstrators, many of them masked, carried banners and chanted "Park Geun-hye, step down" and "No to layoffs" as they occupied a major downtown street and clashed with police, who created tight perimeters with their buses to block them.

Protesters tried to move some of the buses by pulling ropes they tied near the vehicle's wheels, and police, wearing helmets and body armor, responded by spraying tear gas at them. Nearby, police sprayed water cannons from above a portable wall to disperse marchers who were trying to advance.

There were no immediate reports of injuries.

Earlier in the day, members of the Korean Confederation of Trade Unions, an umbrella labor union, clashed with police who unsuccessfully tried to detain KCTU President Han Sang-goon during a news conference. A Seoul court had issued an arrest warrant for Han over a failed court appearance, after he was indicted for his involvement in organising a May protest that turned violent.

"If lawmakers try to pass the (government's) bill that will make labor conditions worse, we will respond with a general strike and that will probably be in early December," said Han, moments before police moved in and forced him to flee inside a building as his colleagues blocked the officers.

Police said the crowd at Saturday's protest was probably the largest at a demonstration in Seoul since May 2008, when people poured onto the streets to protest the government's decision to resume U.S. beef imports amid lingering mad cow fears.

Labor groups have been denouncing government attempts to change labor laws to allow larger freedom for companies in laying off workers, which policymakers say would be critical in improving a bleak job market for young people.

Critics say that the state-issued history textbooks, 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.

Park is the daughter of slain military dictator Park Chung-hee, who ruled South Korea in the 1960s and '70s, and whose legacy as a successful economic strategist is marred by records of severe oppression.

In May, South Korean police detained more than 40 people when protests over the government's labor policies and the handling of a year-old ferry disaster spiraled into violence, leaving several demonstrators and police injured and many police buses damaged.