China is currently battling to contain the virus in several cities, with Shanghai residents simmering under a month-long lockdown and authorities in the capital Beijing closing businesses and residential compounds to quell a nascent outbreak.

In a press conference on Friday, Guangzhou city health authorities said the outbreak had been traced to a worker at the city's Baiyun International Airport, and that they were tracing close contacts to stop the highly transmissible Omicron variant from spreading.

They said 20 COVID cases had been detected through mass tests the day before, and that several areas of Baiyun and Huadu districts would be partially closed off.

They advised citizens against leaving Guangdong, China's most populous province, over the Labour Day holiday, and said those using public transport would need to show results from a PCR test no older than 48 hours.

The April 30-May 4 Labour Day break is one of China's busiest tourist seasons, and the travel industry is taking losses. On Thursday the airport announced it had cancelled flights while staff underwent testing.

Guangzhou authorities said more than 200,000 workers in logistics and deliveries were being tested daily. The city of more than 18 million is a major trade and manufacturing hub.

It has recorded 24 cases in the current outbreak, with 12 symptomatic and 8 asymptomatic cases reported on Friday.

(Reporting by David Kirton; Editing by Jan Harvey)