Four people have died after a massive fire engulfed multiple high-rise towers of a residential complex in Hong Kong's northern Tai Po district on Wednesday, with thick grey smoke billowing out as emergency services battled to subdue the blaze.

Several people remain trapped inside the burning towers, public broadcaster RTHK reported, citing police, while two people are in critical condition having suffered severe burns, it said.

Some fire services staff have also been injured, while trying to put out the flames that ripped through the 31-storey towers.

People gathered on a nearby overhead walkway, watching in dismay as smoke billowed from the buildings, some of which were clad in bamboo scaffolding. Scores of fire engines and ambulances lined the road below the complex, according to Reuters witnesses.

The Fire Service Department told Reuters it does not yet have a figure for the number of people who may still be inside.

The fire department said it received reports at 2:51 pm (0651 GMT) that a fire had broken out in Wang Fuk Court in Tai Po. It was upgraded to a No. 4 alarm, the second highest, at 3:34 pm.

Wang Fuk Court is a housing complex made up of eight blocks, providing close to 2,000 residential units. Several towers have bamboo scaffolding on their exterior.

Hong Kong is one of the last places in the world where bamboo is still widely used for scaffolding in construction.

Hong Kong's Transport Department said that due to the fire an entire section of the Tai Po road, one of Hong Kong's two main highways, has been closed and buses are being diverted.