Tens of thousands of people were being evacuated in southern China and Vietnam on Monday, and dozens of flights cancelled as a typhoon barrelled towards land.

Powerful winds, storm surges and lashing rains were forecast to hammer the southern coastline from Guangdong to Hainan provinces when typhoon Talim makes landfall on Monday night, the China Meteorological Administration said.

The forecaster has issued an orange alert, the second-highest warning in a four-tier colour-coded system, saying the storm was expected to increase in intensity to become a severe typhoon.

Authorities in Vietnam said they were preparing to evacuate about 30,000 people from the areas forecast to be hardest hit in Quang Ninh and Hai Phong provinces from Monday afternoon.

The storm "might be one of the biggest to hit the Gulf of Tonkin in recent years", Vietnam's top disaster response committee said in an online statement.

Tourists have been advised to leave outlying islands and airlines have rescheduled services to avoid the storm.

Prime Minister Pham Minh Chinh directed disaster response teams to prepare for "immediate rescue and relief works" late Sunday, warning of possible floods.

At least 1,000 people were evacuated in Yunfu city in south China's Guangdong province, the state-backed Southern Daily reported.

Around 2:00 pm (0600 GMT), Typhoon Talim was 280 kilometres southwest of Hong Kong, the city's weather observatory said.

Trading on Hong Kong's US$5.2 trillion stock market was cancelled Monday as the Asian financial hub came to a standstill.

The Hong Kong Observatory has warned of possible flooding in low-lying areas due to a storm surge and ferries and most bus services in the city were suspended.

More than 1,000 travellers were affected by flight cancellations and delays, the Hong Kong Airport Authority said.

Authorities in south China's Hainan island asked ships in nearby waters to return to port after the local marine forecasting station warned of waves of up to six metres (20 feet), state news agency Xinhua reported.

Ferry services between Hainan and neighbouring Guangdong province were suspended early on Sunday.

Meilan International Airport and Qionghai Boao Airport, both on Hainan island, have cancelled all flights, state media reported.

Zhuhai Jinwan Airport in Guangdong near Macau cancelled more than 80 flights, local media said.

Scientists have warned that typhoons are becoming more powerful as the world gets warmer with climate change.