HONG KONG, July 1 — China yesterday unveiled details of its contentious new national security law for Hong Kong, ending weeks of uncertainty that have exacerbated concerns over Beijing's erosion of freedoms in the global financial hub.

Beijing passed the legislation yesterday, bypassing the city's local parliament and setting the stage for the most radical changes to the former British colony's way of life since it returned to Chinese rule 23 years ago.

The law defines four crimes: Separatist activity, state subversion, terrorist activity and collusion with foreign forces.

Beijing said the legislation was necessary after sometimes violent anti-government and anti-Beijing protests rocked the city since June last year, plunging it into its biggest crisis in decades. Protesters are angry at what they see as Beijing's tightening squeeze on Hong Kong's affairs.

China denies interfering and accuses Britain and the United States of fomenting the unrest.

Following are details of the law, which took effect at 1500 GMT.

The security law overrides existing Hong Kong laws.