Firefighters on Friday began investigating the cause of a blaze which engulfed a high-rise building in Tsim Sha Tsui overnight.

Around 170 people in the area were moved to safety, but nobody had to be rescued from the Middle Road building, which is under construction.

Two people were taken to hospital after being frightened by the fire, which was spotted shortly after 11pm on Thursday. A total of 250 firefighters and 66 fire engines were sent to the scene.

Deputy chief fire officer Keung Sai-ming said construction materials inside the building made it hard for firefighters to advance.

"When we arrived at the scene, there was already a fire occurring on multi-floors of the construction site. Because it's under construction, there is no fire service installation in commission in the building, except some temporary ducting for us to convey water," he said.

Keung added that because it was windy, the fire spread quickly and fiery debris was blown to five nearby buildings

He said furniture on two balconies caught fire, but because firefighters had anticipated such things, the small fires were quickly extinguished.

Keung added that firefighters were still using jets to try to cool down the high-rise and a team would be checking the building to see if its outer walls and remaining scaffolding are structurally sound.

Debris from the fire came down on the roads below and parts of Nathan Road, Middle Road and Minden Avenue were closed to traffic. Several MTR exits were also shut.

Firefighters said they surrounded the blaze just after 7:30am on Friday and had largely extinguished it around an hour later.

The 48-storey building was due to be completed this year.