The protests in the Asian financial hub began with opposition to a now-suspended extradition law and have evolved into a direct challenge to the government and calls for full democracy.
“The protests and confrontations have spilled over into neighborhoods 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 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.
Australia also warned its travelers in an updated advisory Wednesday.
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 Wednesday.
More protests are planned across the city this weekend, starting Friday with demonstrators planning to rally at the city’s international airport.