SHENZHEN -- China's National Games celebrated a milestone on Sunday as its first cross-boundary torch relay is held simultaneously in Guangdong, Hong Kong and Macao, with one week before the Games opens.

Following the launch ceremony in the southern coastal city of Shenzhen, the torch relay started in Hong Kong, Macao, Guangzhou and Shenzhen - four key cities of the Greater Bay Area.

200 torchbearers from all walks of life will carry the flame, including physicist Xue Qikun and former Olympic diving champion Yang Jinghui.

The "source flame" was extracted and ignited from combustible ice lying more than 1,500 meters beneath the surface of the South China Sea in September.

Following the relay, the torch flames from the four cities will converge in Guangzhou later on Sunday, at Guangdong Olympic Sports Center to be merged into a single flame, which will light the main cauldron at the opening ceremony of the 15th National Games on November 9.