Hong Kong: At least half a million people in Hong Kong are expected to brave sweltering heat to press the government to scrap a proposed extradition law that would allow suspects to be sent to China to face trial, organisers of the march said.

After weeks of growing local and international pressure, the protest is expected to reflect the broad range of opposition to the bill, with many saying they simply cannot trust China's court system or its security apparatus.

Protesters holding umbrellas and placards take part in the rally against the extradition law in Hong Kong. Credit:AP

Among those who joined the march included a wheelchair-bound 78-year-old man, surnamed Lai, who was among the first to arrive at Victoria Park.

"I come here to fight," he said.