The Hong Kong Government Flying Services said it was notified at around 4:05 pm that an oil tanker exploded in the waters 300 kilometres to the east of Hong Kong.

The cause of the explosion was unclear as of Saturday night, a government spokesperson said.

The fire on the oil tanker was put out by the time rescuers arrived, the government spokesperson told AFP, adding that the ship had lost mobility.

Authorities dispatched a fixed-wing aircraft and two helicopters to rescue seven crew members reported to be injured.

One man had already died by the time rescuers arrived at the Panama-registered ship, the 5,547-tonne "Chuang Yi".

Three Indonesian men in their thirties were seriously injured, including one with second-degree burns covering 30 percent of his body and others with burns on their faces.

Two other Indonesian men and a Burmese man, all aged between 30 and 40, had less serious injuries such as lacerations and burns.

Authorities were unable to confirm if there were oil spills because of poor visibility after nightfall, the spokesperson told AFP.