A long-awaited national security trial opens in Hong Kong on Monday for leading China critic and media tycoon Jimmy Lai, who faces possible life imprisonment on charges he colluded with foreign forces, including the United States.

Foreign envoys, business people and legal scholars will be watching the trial closely, saying it looms as a fresh diplomatic flashpoint and a key test for the city's judicial independence and freedoms under the sweeping national security law imposed by Beijing in 2020.

Lai, 76, the founder of now-shuttered pro-democracy newspaper Apple Daily and one of the most prominent Hong Kong critics of China's Communist Party leadership, has faced a salvo of litigation since a wave of pro-democracy demonstrations in 2019.