At least six construction workers have been killed in a fire at a building undergoing renovation in the center of Brussels, Belgian authorities say, in one of the city's deadliest workplace accidents in years.

The blaze broke out on Tuesday morning at the Oxy Tower, near the Place de Brouckère in a busy central district, as Belgium's public broadcaster VRT reported. It started on one of the lower floors and spread into the building's lift shafts, where the six victims were later found. Two other workers were taken to hospital with severe burns.

A rapid, deadly spread

Firefighters brought the initial flames under control relatively quickly, but the fire had already reached the elevator shafts, which acted as channels carrying smoke and heat through the structure, according to reporting on the incident. Rescuers using thermal cameras and search dogs worked to reach two lift cars that had become trapped. Recovering the bodies from the shafts proved slow and difficult.

Around 250 people were working on the site at the time and were evacuated, authorities said. The Red Cross provided support to shaken workers gathered nearby.

Investigation under way

Prosecutors in Brussels have opened an investigation into the fire, Euronews reported, and the cause is not yet known. Belgium's King Philippe visited the scene, and senior government figures expressed shock at the loss of life.

The Oxy Tower, a high-rise dating from the 1970s that once housed offices including the Belgian postal service, is being redeveloped into a mixed-use complex. Buildings undergoing major renovation can present particular fire risks, as protective systems may be partially disabled and materials left exposed during works, though investigators have not said what role, if any, such factors played here.

For now, the focus is on establishing how the fire spread so quickly and claimed so many lives. The toll, which authorities have described as provisional, has made the fire one of the worst construction-site disasters Brussels has seen, and has prompted questions about safety on major building projects in the heart of the Belgian capital.