Hong Kong travel agencies have started cancelling package tours to Bangkok because of violent anti-government protests as the Security Bureau raised the travel threat level to "red" - the second highest warning.
Video: Police fire rubber bullets as unrest continues in Bangkok
About 80 tours involving 1,000 people will be affected. A lower "yellow" warning has been placed on the rest of Thailand.
The executive director of the Travel Industry Council, Joseph Tung Yao-chung, announced the cancellation of most tours to Bangkok starting from today until December 13.
The bureau said travellers should consider changing their existing plans or avoid all non-essential travel. "Those already there should monitor the situation, attend to personal safety and avoid protests and large gatherings of people," a government spokesman said.
The move came as Prime Minister Yingluck Shinawatra rejected protesters' demands to suspend the country's democratic system.
She indicated she would not resign despite continuing clashes between security forces and demonstrators bent on toppling her government.
Police used rubber bullets, tear gas and water cannon against rock-throwing demonstrators as they intensified their defence of key government buildings, after weekend unrest in the capital left several dead and more than 100 wounded. The protests, aimed at unseating the elected government and replacing it with a "people's council", are the latest outbreak of civil strife to rock the kingdom since royalist generals ousted Thaksin Shinawatra, Yingluck's brother, seven years ago.
Bloodshed in the capital in recent days is the worst political violence in Thailand since a deadly 2010 military crackdown on pro-Thaksin "red shirts".
It has also raised fears of damage to the economy, particularly the lucrative tourist sector as the peak season gets under way.
The major flashpoints are just a few kilometres from Bangkok's main backpacker area.
In her first televised address since the protests descended into violence late on Saturday, Yingluck said she could not give way to the demands of the protest leaders because they would breach the country's laws.
"I don't want to hold on to power. Anything I can do to bring back peace, I'm willing to do ... but what I can do must be under the constitution," she said.
She said she would have considered resigning or calling an election if protesters had not already ruled out these moves as insufficient, insisting the government was open to "every option" to restore peace.
Protest leader Suthep Thaugsuban, who had talks with Yingluck on Sunday night, has said he will not be satisfied with her resignation or new elections.
Instead, he wants an unelected "people's council" to pick a new prime minister, even though Yingluck was elected with an overwhelming majority.
Agence France-Presse, Reuters, Associated Press