People piled into supermarkets on Tuesday, leaving little on the shelves, as panic buying set in and residents stocked up on necessities for fear that shops could be closed for two days.
Windows in homes and businesses across the city were taped up, with residents hoping it could help reduce the impact of any shattered glass.
Ragasa, packing hurricane-force winds of up to 220km/h, is posing a "severe threat to the coast of Guangdong", the Hong Kong Observatory said, referring to the Chinese province that neighbours the financial hub.
It will maintain super typhoon intensity as it edges closer to the coast of Guangdong, and as it impacts Hong Kong, mainland China and Taiwan, after sweeping through the northern Philippines on Monday.
Hong Kong issued the typhoon signal 8, its third highest on Tuesday afternoon, which urges most businesses and transport services to shut down.
More than 700 flights have been disrupted, including in the neighbouring gambling hub of Macau and in Taiwan.
The weather is expected to deteriorate rapidly later on Tuesday and the observatory said it will assess whether to issue a higher warning late on Tuesday or early Wednesday.
Hurricane-force winds offshore and on high ground were likely in Hong Kong on Wednesday, with heavy rain expected to lead to a significant storm and sea surge in the densely packed city.
It warned of rising sea levels, which it said would be similar to those seen during Typhoon Hato in 2017 and Typhoon Mangkhut in 2018, both of which caused billions of dollars in damage.
Water levels will rise about two metres along Hong Kong's coastal areas and maximum water levels could reach 4m-5m in some areas, the observatory said, urging residents to take appropriate precautions.
Local authorities handed out sandbags for residents to bolster their homes in low-lying areas, while many people stockpiled daily necessities.
Hong Kong's Stock Exchange will remain open.
At Ragasa's peak intensity on Monday, maximum sustained winds near its eye topped 260km/h, making it the world's most powerful category five storm in 2025.
The typhoon has since weakened slightly but is still capable of wreaking havoc on the densely populated Chinese coast as a category four typhoon.
Chinese authorities have activated flood control measures in several southern provinces, warning of heavy rain from late on Tuesday.
More than 10 cities in Guangdong, including technology hub Shenzhen and coastal city Zhuhai had suspended work, transport services and schools due to warnings of storm surges and high waves.
China's Environmental Forecasting centre said that coastal waters off Guangdong would be hit by huge to extremely rough waves with heights of up to 7m.
Authorities in Shenzhen have prepared more than 800 emergency shelters, while in the city's Nanshan district, teams were chainsawing tree branches along main roads in preparation for the typhoon.
Residents in the world's largest gambling hub of Macau also braced for significant impact, with its casinos to be forced to shut late on Tuesday afternoon when the former Portuguese colony lifts its typhoon signal to 8.
Taiwan's government has evacuated more than 7600 people from mountainous southern and eastern areas, while transport disruptions continued for a second day on Tuesday with 273 flights cancelled and some rail services suspended.
