Local media showed severe flooding had left cars underwater and people swimming in Macau's city streets, with the territory's mega-casinos running on back-up generators.
The Macau government said one of the men died after being injured by a wall that blew down, another fell from a fourth floor terrace and another was a Chinese tourist hit by a truck. Details on the two others who died were not immediately available.
Apple Daily showed footage of people swimming through muddy water in what are usually roads, and being swept off their feet by winds.
The sprawling Venetian casino resort was on back-up power and without air conditioning or proper lighting, said one person.
#TyphoonHato #Hato #HongKong much serious than i thought...the water level keeps rising pic.twitter.com/k5Dizol0hk — Mosyroro (@mosyroro) August 23, 2017
One employee of Sands, which owns the Venetian and the Parisian, said power had been out across the whole of Macau but was beginning to return.
"Because many guests come in the summer, a lot of them have been stuck in the major resorts and casinos," the employee said.
"All transportations - air, ground, sea - have halted, so customers who have checked out cannot leave yet."
Electricity was still down at the Grand Lisboa Wednesday afternoon, with the casino and restaurants there out of action, a staff member told AFP.
Source: LUSA / AAP
Residents took to social media to complain about city-wide power and mobile phone network outages.
Brian Chan, 31, said authorities had failed to give enough notice of the impending storm and were not properly prepared, describing the territory as "totally lost" in the typhoon.
The water supply was also limited, authorities said, and 50 flights cancelled from its international airport.
By evening, parts of Macau were still without power.
"Some have no tap water supply. The city looks like after an attack," Harald Bruning, editor of the Macau Post Daily, told AFP, describing it as the worst typhoon he had experienced in 30 years.
Hurricane winds and heavy rain had earlier hit Hong Kong, leaving an 83-year-old man dead after he fell into the sea, police said, and more than 120 injured.
The typhoon shut down the stock market and forced the cancellation of hundreds of flights in the worst storm the city has seen for five years.
'Flying trees'
Meteorologists raised the city's most severe Typhoon 10 warning as the storm hit, only the third time they have done so since 1997, when the former British colony was handed over to China.
The storm passed as close as 60 kilometres (37 miles) and made landfall at noon (0400 GMT) in the southern mainland Chinese city of Zhuhai.
Thousands of people were evacuated Tuesday in parts of south China in preparation for the typhoon's arrival, the official Xinhua news agency said.
Hato sent metres-high waves crashing into Hong Kong's shorelines with flooding knee deep in some areas.
Gusts of up to 207 kilometres per hour brought flying debris, tearing down trees and scaffolding and smashing skyscraper windows.
Fallen trees cut off roads to parts of the territory, with the city's popular Victoria Park covered in a mass of strewn branches.
"I was on my balcony in the village of Yuen Long when a tree literally flew past my house," said Dave Coulson from the rural northwestern New Territories, who added he was having frequent power cuts.
More than 400 flights were cancelled, with flag carrier Cathay Pacific axing most of its departures until 5:00 pm (0900 GMT).
The airline said it had begun to reschedule the flights with some taking off Wednesday evening.
As the storm moved away, the observatory gradually cancelled all typhoon signals, although it said there would still be strong offshore winds and the rain continued.
Hong Kong is regularly besieged by typhoons between July and October, but direct hits are rare.
The city saw its strongest storm in 1962 when the eye of typhoon Wanda passed over and gusts of 284 kilometres per hour were recorded.
It killed 130 people and destroyed thousands of residential huts, leaving 72,000 people homeless.
