Chinese president and Communist Party leader Xi Jinping has led other top officials in paying respects to the founder of the communist state Mao Zedong ahead of a massive celebration of the People's Republic's 70th anniversary.

But in Hong Kong, demonstrators denigrated the Chinese dictator, who historians say killed millions during purges, mass executions and state-induced famines. Doormats labeled "step on me" with Mao's picture have been festooned all over Hong Kong for the anniversary.

Monday's unusual move saw Xi bow three times to Mao's statue at the former leader's mausoleum in the center of Beijing's Tiananmen Square and pay his respects to Mao's embalmed corpse that has lain in state in the hulking chamber since soon after his death in 1976.

Xi also ascended the nearby Monument to the People's Heroes to pay further tribute on what has been designated Martyr's Day, just ahead of Tuesday's National Day festivities to be marked by a massive military parade through the center of the city of 20 million people.