MASKED protesters have streamed into central Hong Kong after the city’s embattled leader invoked rarely used emergency powers to ban masks at rallies in a hardening of the government’s stance after four months of demonstrations.

Immediately defying the ban set to take effect today, thousands of protesters filled the streets in the central business district shouting “Hong Kong, resist”.

City chief executive Carrie Lam said that the mask ban, imposed under a colonial-era emergency ordinance that was last used over half a decade ago, targets violent protesters and rioters and “will be an effective deterrent to radical behaviour”.

The ban applies to all public gatherings, both unauthorised and those approved by police. Masks will be permitted for “legitimate need” when wearers can prove they need them for work, health or religious reasons.

MEANWHILE, investigators are searching for possible motives for the knife attack at Paris police headquarters as the French government said there is nothing to suggest the police employee who stabbed four colleagues to death was radicalised.

The assailant, a 45-year-old technology administrator in the intelligence unit of the Paris police, was shot dead after Thursday’s attack.

Government spokeswoman Sibeth Ndiaye said prosecutors have decided to open a murder investigation on facts “which are not falling under terrorism at this stage of the investigation”.

Investigators are scouring the attacker’s computer for a motive.

READ MORE: Paris police headquarters attack leaves at least four officers dead

ELSEWHERE, Iraq’s top Shiite cleric has sharply criticised the government over deadly violence gripping the country, urging political leaders and protesters to pull back “before it is too late”.

The highly anticipated comments by Grand Ayatollah Ali al-Sistani came as the death toll in this week’s anti-government demonstrations climbed to 42.

His sermon came hours after Iraq’s prime minister called on protesters to go home, comparing security measures to “bitter medicine” that needs to be swallowed.

FINALLY, a pilot with more than 7000 hours of experience flying a B-17 and his co-pilot were among seven people killed when the bomber crashed after encountering mechanical trouble on takeoff.

Pilot Ernest McCauley, 75, of Long Beach, California, had flown for over 20 years with the educational group that owned the Second World War-era plane and was also its safety officer, according to the National Transportation Safety Board.

Five passengers were killed along with McCauley and the co-pilot, according to the Connecticut Department of Emergency Services and Public Protection.

Investigations have begun.