Chinese leaders endorsed a sweeping overhaul of Hong Kong's electoral system Tuesday, slashing its number of directly elected seats and ensuring a majority of the city's lawmakers will be selected by a reliably pro-Beijing committee.

The new measures, which bypassed Hong Kong's legislature and were imposed directly by Beijing, are the latest move aimed at quashing the city's democracy movement after huge protests.

"President Xi Jinping signed presidential orders to promulgate the amended annexes," China's official Xinhua news agency said in a short report.

Hong Kong's 7.5 million residents are still not sure what the new law contains with no details yet published.

But Tam Yiu-chung, Hong Kong's sole delegate on China's rubber-stamp parliament, gave a breakdown of what the new measures included.

"The amendments were unanimously passed by 167 members of the Standing Committee of the National People's Congress," he told AFP.

Under the new law, Hong Kong's legislature will be expanded from 70 to 90 seats.

Only 20 of those seats will now be directly elected, down from 35, Tam said. The majority -- 40 -- will be chosen by a reliably pro-Beijing committee.

The remaining 30 will be chosen by "functional constituencies" -- bodies representing certain industries and special interest groups that have also been historically loyal to Beijing. 

Anyone standing for election will also have to be vetted for their political views.

Tam revealed that the vetting committee would be created by authorities in Hong Kong and the city's new national security apparatus would have a say in who gets approved.

"The National Security Committee and the National Security Police will provide reports on every single candidate to assist the vetting by the qualification review committee," he told AFP.