The 20th straight weekend of anti-government protests in Hong Kong again saw the city's police force become a major target as rioters went on a destructive rampage across multiple districts in Kowloon on Sunday.

The rampage followed an illegal procession that defied a police ban after the police unearthed intelligence indicating that radical rioters would launch deadly attacks.

The police deployed a remote-controlled bomb disposal robot to detonate a carton box suspected to contain explosives. The box, with electric cables fastened around it, was placed on the road just a block from Sham Shui Po police station.

It was the second time in a week that explosive devices had been found during protests. On Oct 13, a homemade bomb that was remotely detonated with a mobile phone, went off in a flower planter at the junction of Nathan Road and Fife Street in Mong Kok.

The police also seized 42 gasoline bombs and raw materials used for creating paintballs from two vehicles in Tai Po on Sunday. The bombs were thought to have been destined for use by rioters across Kowloon. Two men, aged 31 and 34, were arrested at the scene.

A video recorded a black-clad masked thug hurling a gasoline bomb from a flyover in Prince Edward onto police officers assembled below. An officer caught fire, but the fire was immediately put out.

At least two police stations — in Tsim Sha Tsui and Sham Shui Po — came under severe attack on Sunday afternoon as mobs hurled more than a dozen gasoline bombs at them.

Spikes were seen being placed along Nathan Road in a bid to impede police operations after the stand-offs turned into violent clashes.

As night fell in Mong Kok, police vehicles were showered with bricks tossed by mobs of thugs, shattering their windows.

According to the police, 351 officers had been injured so far since the protests erupted on June 9.