COPENHAGEN, Denmark (AP) -- A fire raged through one of Copenhagen's oldest buildings Tuesday, destroying about half of the 17th-century Old Stock Exchange and collapsing its iconic dragon-tail spire, as passersby rushed to help emergency services save priceless paintings and other valuables.

The blaze broke out on the building's roof during renovations, but police said it was too early to pinpoint the cause. The red-brick building, with its green copper roof and distinctive 56-meter (184-foot) spire in the shape of four intertwined dragon tails, is a major tourist attraction next to Denmark's parliament, Christiansborg Palace, in the heart of the capital.

Bells tolled and sirens sounded as fire engulfed the spire and sent it crashing onto the building, which was shrouded by scaffolding. Huge billows of smoke rose over downtown Copenhagen and could be seen from southern Sweden, which is separated from the Danish capital by a narrow waterway.

"A piece of Danish history is on fire," Prime Minister Mette Frederiksen wrote on Instagram, saying that it hurt to see the loss of such "irreplaceable cultural heritage."

Ambulances were at the scene but there were no reports of casualties.

Firefighters, who reportedly pumped water from a nearby canal, sprayed water through the doorway of the Old Stock Exchange's gilded hall that is used for gala dinners, conferences and other events and where many paintings were on display.

Danish Culture Minister Jakob Engel-Schmidt said it was "touching" to see how many people lent their hand "to save art treasures and iconic images from the burning building." One man jumped off his bicycle to help soon after the fire broke out, and members of the public helped first responders to carry huge works of art to safety.

Among the pieces that had been on display in the building was a huge painting completed in 1895 by Danish artist P.S. Krøyer called, "From Copenhagen Stock Exchange." No information has been released about which works of art were saved from the blaze, although video footage appeared to show the Krøyer painting being removed.

Brian Mikkelsen, chief of the Danish Chamber of Commerce, which is headquartered in the Old Stock Exchange and owns the building, was seen with his staff scrolling through a binder of photos of paintings to be saved. Works were carried to the nearby parliament and national archive building. Rescuers used crowbars and other tools to remove valuables and save them from the fire, Mikkelsen said.

"We have been able to rescue a lot," a visibly moved Mikkelsen told reporters. "It is a national disaster."

Jakob Vedsted Andersen, a Greater Copenhagen Fire Department spokesman, said the fire began on the roof Tuesday morning and quickly spread, collapsing parts of the roof and destroying about half of the building. He said no other buildings were at risk but that it could take firefighters 24 hours to secure the scene.

Tim Ole Simonsen, another fire department spokesman, said "the fire started in the part of the building where work has been going on, but that's all I can say about it."

René Hansen of the coppersmith company that was renovating the roof told broadcaster TV2 it had 10 people on the roof when the fire alarm went off.

"After five minutes, smoke began to rise from the floor to the ceiling," Hansen said.

Tommy Laursen of the Copenhagen police said it was too early to say what caused the fire and that officers would be able to enter the building in "a few days."

Up to 90 members of an army unit were deployed to cordon off the area and "secure valuables," Denmark's armed forces said.

King Frederik wrote on Instagram that "an important part of our architectural heritage" was being destroyed. "This morning we woke up to a sad sight," he wrote.

The exchange was built in 1615 and is considered a leading example of Dutch Renaissance style in Denmark. The Chamber of Commerce moved into the building after Copenhagen's stock exchange left in 1974.

The roof, masonry, sandstone and spire were being renovated, and Mikkelsen said there had been plans for the royal family, government officials and other dignitaries review the work later this year.

"That won't happen now," he said.

The future of the structure was unclear, but Engel-Schmidt, the culture minister, wrote on the social platform X that he would do everything he could "so that the dragon spire will once again tower over Copenhagen," describing it as "a symbol of Denmark's strong history as a trading nation."

The adjacent Christiansborg Palace has burned down several times, and in 1990 a fire broke out in an annex of the Danish parliament, known as Proviantgaarden but the Old Stock Exchange was unscathed.

Police closed a main road in Copenhagen and warned on X that the public should expect the area to be cordoned off for some time. Several bus lines were rerouted and Danish media reported huge traffic jams.

Queen Margrethe, who turned 84 Tuesday, toned down the celebrations because of the fire, broadcaster TV2 said. A band with the Royal Life Guard had been scheduled to play for the former monarch outside the Fredensborg Castle, where she is staying for the spring and summer, but that was canceled.

The fire in Copenhagen was reminiscent of a April 2019 blaze at Notre Dame. The 800-year-old cathedral in Paris also lost its spire. Its restoration is slated for completion this year. In November 1992, soldiers and workers scrambled to save priceless works of art when Windsor Castle in England was consumed in flames. That fire destroyed the state dining room and other parts of Queen Elizabeth II's weekend home.