Cairo, Egypt (CNN) -- A fire broke out in the Egyptian Interior Ministry on Tuesday in downtown Cairo following a protest earlier in the day.
Flames could be seen on the roof of the multistory building, and a dark plume of smoke loomed over the city. People could be seen fleeing the building as it burned. The blaze was extinguished in under an hour.
The ministry was the site of a peaceful protest Tuesday morning and afternoon, with thousands of ministry employees -- many of them police officers -- making demands, mainly for higher wages.
Protesters at the building denied setting the fire, saying it originated inside. During the protest, some of them could be seen climbing on guard posts and the building's roof.
"I suspect that an electrical circuit malfunction may have caused the fire because it started at the top floors of the police communication building inside the ministry," said Alla Mahmoud, Interior Ministry spokesman. "The protesters did not enter."
He said uniforms and old furniture are stored on the top floors, which would explain the thick smoke.
The cause of the fire was under investigation, he said, and findings will be announced Wednesday morning.
Several firefighters suffered problems due to smoke inhalation, a Ministry of Interior spokesman said. Another man was rushed away from the building in an ambulance, but the cause of his injuries was not clear.
Before the fire broke out, a procession of thousands of demonstrators made its way from the Interior Ministry through Cairo's Tahrir Square -- ground zero for protests that toppled longtime Egyptian President Hosni Mubarak last month -- and in the direction of the state television and radio offices.
In a similar protest a few weeks ago, demonstrators set other buildings in the Interior Ministry complex ablaze, as well as cars. However, that fire did not grow to the size of Tuesday's blaze.
CNN's Christine Theodorou and journalists Ian Lee and Mohamed Fahmy contributed to this report