A fire broke out Wednesday at a factory making costumes for Rio de Janeiro's Carnival, injuring 21 people in a blow to the famed extravaganza that attracts millions of tourists to the Brazilian city every year.

Firefighters scaled ladders to reach a window where desperate workers were calling for help as black smoke bellowed from the building in the north of the city, local media images showed.

The area around the factory was cordoned off by authorities as firefighters brought the blaze under control, according to an AFP reporter.

The fire department's communication service told AFP that 21 people were hospitalized, 12 of whom were in a serious condition.

Earlier, state health secretary Claudia Mello said at least eight people had been intubated and were on artificial respiration.

Fire department chief Colonel Luciano Pacheco Sarmento said that those affected were working in a "precarious manner" and without "safety conditions."

The building contained "a lot of highly combustible material," added Sarmento.

"We have information that there have been fires here before," he said.

'No way' down

A survivor, identified as Roberta, told local media she had been working and sleeping in the building "since Monday."

The fire "came from the floor below and we had no way to get down," she said.

Rio de Janeiro's labor ministry announced a probe into working conditions at the factory.

The cause of the fire has not been established.

Rio's Carnival, famous for parades with lavish costumes and towering floats to the tune of samba music, begins on February 28 and will run until March 8.

Preparations last almost the whole year, with the final weeks often very tense as competitors scramble to meet deadlines for the making of costumes and floats.

One of the associations for the samba schools that compete in the parades, Liga RJ, expressed its "deep concern" for the injured.

The organization said the Maximus Factory that was hit by the fire was "an essential space for the Rio Carnival."

"The impact of this incident directly affects the planning of the Carnival and the entire production chain of its realization," Liga RJ warned in an Instagram message.

"The League will urgently call its presidents for an extraordinary general assembly to evaluate the situation," the statement said.

Samba schools affected

Three samba schools were having their outfits made at the affected factory, although none of them were taking part in the main competition for Carnival champion.

Like football, the parade competition has several divisions, and samba schools can be relegated or rise up through the ranks each year.

Rio de Janeiro Mayor Eduardo Paes said the schools impacted by the fire would not be demoted from their carnival league.

"If they can parade, all three will do so out of competition," he wrote on the X social media network.

Paulo Santi, director of Imperio Serrano, one of the affected schools, said it would carry out its planned parade on March 1 "as if it were competing for the title. Showing the people of Rio that Imperio Serrano will endure."

The samba schools are rooted in Rio's favela urban settlements and each parade tells a story, often dealing with politics, social issues and history.

Their parades take place in the Sambadrome, a large, open-air venue where more than 70,000 spectators gather to watch the spectacle with thousands of dancers in shimmering costumes.

In 2011, a blaze in the Samba City complex of workshops and warehouses stocking Carnival material wiped out eight months of preparations worth millions of dollars.