Police armed with pepper spray and batons have clashed with demonstrators in Hong Kong as fears grow security forces may move in to clear the streets.

As huge crowds rallied overnight in the city's business district to press their demand for wider political reform, Hong Kong's top leader, Chief Secretary Leung Chun-ying, on Saturday urged everyone to go home and said things needed to get back to normal by Monday.

He says the government and police have "the duty and determination to take all necessary actions to restore social order."

Large crowds of protesters scuffled with police in the early hours Sunday in the blue-collar Mong Kok district, a flashpoint that has seen violent clashes between pro-democracy student protesters and their opponents.

There was no word on casualties.