A tropical storm is intensifying and is expected to reach typhoon strength before hitting southern China's coast on Sunday.

Hong Kong issued its third-highest tropical cyclone warning in the early hours of Sunday as Typhoon Wipha (locally named Crising in the Philippines) drew nearer, with authorities cancelling classes and grounding hundreds of flights.

Wipha intensified into a severe tropical storm as it blew away from the Philippines on Saturday, bringing strong winds and heavy rains to many areas, including Metro Manila.