China has highlighted security risks for its citizens visiting Australia, the United States and nine other countries in a travel warning which will worry tourism operators becoming increasingly dependent on booming Chinese visitor numbers.

China's Foreign Ministry issued the travel advice on a social media account ahead of the current long weekend in China, which is a popular time for families to travel overseas. In a series of posts over several days, it issued security warnings for Australia, the US, South Korea, Vietnam, Cambodia, South Africa, Congo, Thailand, Egypt and East Timor.

The inclusion of Australia and the US on the list suggests the postings could be politically motivated; Beijing has previously used warnings about student safety in countries like Australia as a subtle way to exert pressure on the government via the education sector. US president Donald Trump has announced trade tariffs against China.

China overtook New Zealand as the largest source of tourists visiting Australia for the 12 months to February. Peter Morris PMZ

However, the advice on Australia posted on the Consular Affairs bureau's WeChat account did not specify what the security concerns were. It was also not picked by China's state-run media, which suggests there is not a wider campaign to discredit the Australian or US tourism industries. China last year banned group tours to South Korea following a political dispute between the two countries over Seoul's deployment of a US anti-missile system.

The travel advice on Australia was posted on April 28. It highlighted a seminar held with travel agencies at China's Consulate in Melbourne last week. The post said Chinese travel agents were briefed on security "incidents" involving Chinese citizens in Australia. Vice-Consul Sun Yan asked the travel agencies to advise Chinese tourists on how to avoid security risks. Mr Sun also advised travel agents to ensure they had an emergency communication plan to contact the Consulate if there was a security incident involving their clients.