By Jessie Pang and James Pomfret

HONG KONG, March 1 (Reuters) - Hundreds of people gathered outside a Hong Kong court on Monday ahead of the hearing of 47 democracy activists charged with conspiracy to commit subversion, as authorities intensify a crackdown under the city's national security law.

The activists are accused of organising and participating in an unofficial primary poll last July aimed at selecting the strongest candidates for a legislative council election that the government later postponed, citing the coronavirus.

Authorities said the informal poll was part of a plan to "overthrow" the government.

"This is the most ridiculous arrest in the history of Hong Kong," said Herbert Chow, 57, who was queuing outside the court and wearing a black face mask.

"But I have confidence in our judicial system to restore justice. It’s the last line of defence."

Security was tight as supporters gathered before dawn outside the West Kowloon court in one of the largest rallies since the coronavirus outbreak.

"I've been here since 5 a.m. We have been taking shifts since yesterday. Our friend is among those charged," said Kristine, 20. "I want to tell my friend that we are willing to sacrifice ourselves for our city."

Some supporters held up large yellow banners that said: "Release all political prisoners now."

The activists - 39 men and eight women aged 23-64 - were charged on Sunday under the national security law which punishes what China broadly defines as secession, subversion, terrorism and collusion with foreign forces with up to life in prison.

Among those charged was the organiser of the primary election and former law professor Benny Tai as well as veteran activists Lester Shum, Joshua Wong and Owen Chow.

The charges are the latest blow to the city's pro-democracy movement. Since the security legislation was imposed on the city last June, some elected legislators have been disqualified, scores of activists arrested and others have fled overseas.

As Beijing consolidates its hold over Hong Kong, concern is mounting in the West over freedoms promised to the former British colony when it returned to China in 1997 and which underpin its role as a global financial centre. (Reporting By Jessie Pang and James Pomfret; Writing by Anne Marie Roantree)