A man who was doused with flammable liquid and set alight by radical protesters in Hong Kong on Monday was still in critical condition, a spokesman for the Hospital Authority said on Tuesday.

The 57-year-old man suffered more than 40 percent burns and is under close medical supervision in the intensive care unit.

Police have classified the case as attempted murder, a charge which carries a maximum penalty of life imprisonment. They are also appealing for any witnesses to come forward and provide information on the incident.

The spokesman also said that a protester who was shot with live ammunition in the Sai Wan Ho area on Monday morning had his medical condition downgraded from critical to serious on Tuesday. A traffic police officer, who shot and wounded the black-clad rioter during a scuffle, had acted in "a split second" to protect his life, as well as those of others, when the protester tried to snatch his gun, according to Hong Kong police.

Hong Kong was plunged into citywide chaos for a second straight day, amid violent actions by radical protesters in multiple districts calling for a "general strike". Like the day before, they disrupted the morning commute by blocking subway lines, setting up barricades and scattering nails on roads to block private cars and buses.

Service on four major subway lines that transport commuters into Hong Kong Island from Kowloon and the New Territories had either been suspended or delayed, subway operator MTR Corp said on its website.

A train on the East Rail Line was forced to stop in the middle of operation after obstacles were found on the tracks. The commuters had to walk on the rail track to get back to the nearby Sha Tin station.

Public buses had to cease operations in the middle of roads after being trashed and painted with graffiti on windshields. About 30 buses were forced to park along Nathan Road at Mong Kok as their tires were punctured by protesters.

Radicals also threw bricks and other hard objects from high places, such as overpasses, onto roads where cars and pedestrians were passing through, forcing police to fire tear gas to disperse them. At least one man was taken to hospital with head injuries after being hit by an object thrown from a footbridge over Pok Fu Lam Road near the University of Hong Kong.