* Destructive winds, waves batter Hong Kong, south China
* Power blackout, flooding in Macau, three dead
* Financial markets, schools, businesses closed
* Hundreds of flights cancelled in HK and mainland China
* Worst storm in five years (Adds storm warning downgrade in HK as typhoon moves west)
By James Pomfret and Anne Marie Roantree
HONG KONG, Aug 23 (Reuters) - Typhoon Hato, a maximum category 10 storm, slammed into Hong Kong on Wednesday lashing the Asian financial hub with wind and rain that uprooted trees and forced most businesses to close, while in some places big waves flooded seaside streets.
There were reports of 34 people injured in Hong Kong while in the city of Macau, across the Pearl River estuary, three people were killed, authorities there said.
In Hong Kong, more than 450 flights were cancelled, financial markets suspended and schools closed as Hato bore down, the first category 10 storm to hit the city since 2012.
"I've never seen one like this," Garrett Quigley, a longtime resident of Lantau island to the west of the city, said of the storm.
"Cars are half submerged and roads are impassable with flooding and huge trees down. It's crazy."
Many skyscrapers in the usually teeming streets of Hong Kong were empty and dark as office workers stayed at home.
Hato, that means "sky pigeon" in Japanese, churned up Hong Kong's Victoria Harbour and triggered large swells and big waves on some of the city's most popular beaches, with serious flooding in low-lying areas.
In residential districts such as Heng Fa Chuen on densely populated Hong Kong island, waves smashed against the sides of oceanfront buildings and surged over a promenade, sweeping away walls and benches and swamping vehicles parked nearby.
Construction cranes swayed at the tops of skyscrapers, windows imploded and nearly 200 trees were uprooted, while some people used canoes to venture out into flooded streets.
Authorities downgraded the storm to a category three by late-afternoon with government services, the courts, financial markets and companies set to resume normal business on Thursday.
HIGH SEAS
The storm also caused a power blackout across most of the gambling hub of Macau for about two hours, residents said, with disruption to mobile phone and internet networks. There was severe flooding on the streets, with some cars almost completely submerged, and the water supply was affected in some districts. The three men who died included a 45-year-old Chinese tourist who was hit by a heavy truck, according to a government statement.
The former Portuguese colony's casinos, however, had backup power, two casino executives told Reuters.