Hundreds of thousands of protesters took to the streets in Hong Kong to demonstrate against a controversial extradition law that would allow suspects to be sent to mainland China.

Protesters carrying banners denouncing the law and demanding the resignation of Chief Executive Carrie Lam’s defied thirty degree heat to march two miles to the city’s Legislative Council on Sunday.

Organisers estimated more than a million people attended the march, which flooded the city’s public transport network and led to widespread congestion. Police said the crowd reached 240,000 at its peak.

The proposed law would enable the Beijing government to extradite fugitives in Hong Kong to mainland China. Hong Kong currently limits extraditions to jurisdictions with which it has existing extradition agreements or to others on an individual basis under a law passed before 1997.