The blaze at the World Trade Center in Causeway Bay injured at least 13 people, including one who was semiconscious, the police said.

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HONG KONG — Hundreds of people were trapped for hours on the roof of a commercial building in Hong Kong after a fire broke out on Wednesday, injuring at least 13 people and forcing firefighters to rescue many by ladder.

The fire began about 12:30 p.m., during lunch hour, at the World Trade Center in the crowded neighborhood of Causeway Bay on Hong Kong Island. The 38-story building houses offices, restaurants and a shopping mall on its lower floors.

More than 300 people were trapped on the roof for at least three hours, the public broadcaster RTHK reported. By late afternoon, more than 1,200 people had been evacuated from the building, the police said.

At least 13 people were sent to hospitals for treatment, many for smoke inhalation, including one person who was semiconscious.

The authorities did not immediately reveal the cause of the fire. The South China Morning Post newspaper reported that a preliminary investigation suggested it had broken out in an electrical switch room on the first floor, then spread to scaffolding surrounding parts of the building.

Photos and video footage shared on social media showed dense smoke wafting from the lower floors. People crowded onto roofs and outdoor terraces as they awaited rescue.

Rescue crews were seen treating people on stretchers in the street.

Firefighters used extendable ladders to rescue people, and they deployed two water jets and two teams equipped with breathing apparatuses to fight the blaze, the government said.

Causeway Bay is one of the busiest commercial districts in Hong Kong, filled with shops, restaurants and malls near Victoria Harbor, which separates Hong Kong Island from the Kowloon Peninsula.

The authorities closed nearby streets to help fight the blaze and evacuate people.

Last year, seven people were killed and more than a dozen were injured after a fire broke out at an unlicensed restaurant in the Jordan neighborhood of Hong Kong. The fire was believed to have been started by candles that had been lit to celebrate a birthday and the Diwali festival.