After Australia also warned its travellers in an updated advisory on Wednesday, August 7 US also raised its travel warning for Hong Kong, urging travellers to exercise increased caution in the Chinese territory due to what it described as civil unrest after months of frequent violent street protests.
The protests in the Asian financial hub began due to extradition law which is now-suspended. Later the protest has evolved into a direct challenge to the government and calls for full democracy.
"The protests and confrontations have spilt over into neighbourhoods other than those where the police have permitted marches or rallies," said the advisory, which was posted on the U.S. Consulate General Hong Kong and Macau's website on Wednesday.
"These demonstrations, which can take place with little or no notice, are likely to continue," it said. The advisory was raised to level two on a four-point scale.
The protests pose the biggest popular challenge to Chinese President Xi Jinping since he came to power in 2012. Xi is also grappling with a debilitating trade war with the United States and a slowing economy.
Hong Kong is facing its worst crisis since it returned to China from British rule in 1997 because of the protests, the head of China's Hong Kong and Macau Affairs Office said on Wednesday.
More protests are planned in several districts across the city this weekend, starting on Friday, with demonstrators also planning a three-day rally at the city's international airport.
Hong Kong's embattled leader Carrie Lam visited Hong Kong districts on Wednesday to speak with residents and inspect a police station that had been the target of recent protests.
She said in a statement after the visit the government would put forward measures to improve people's livelihoods.
Young people have been at the forefront of the protests and are angry about broader problems that include sky-high living costs and what they see as an unfair housing policy skewed towards the rich.
The normally efficient and orderly city has seen its transport network besieged and shut down by demonstrators, while protests across the city have also shut big-brand stores and popular shopping malls.
Hong Kong police have arrested 589 people since the protests began in June, the youngest aged 13.
Several thousand Hong Kong lawyers, dressed in black, marched in silence on Wednesday to call on the government to safeguard the independence of the city's department of justice.
They fear the justice department's prosecutions of arrested protesters are taking on an increasingly political slant. Many of those arrested have been charged with rioting, which carries a 10-year jail term.
Protesters have started to use increasingly diverse tactics to evade capture, shifting quickly from place to place and using online platforms such as Telegram to direct hundreds of people.
They also circulated brightly coloured pamphlets for tourists ahead of the airport demonstrations to help them understand what was happening. The pamphlets said the protesters would never surrender.
"Dear Travellers, please forgive us for the 'unexpected Hong Kong'. You arrive in a broken, torn-apart city, not the one you have once pictured. Yet the city you imagined is exactly what we are fighting for," the pamphlets said.