Denmark's historic old stock exchange building in the centre of Copenhagen has been engulfed by fire.

The 17th Century Børsen is one of the city's oldest buildings and onlookers gasped as its iconic spire collapsed in the flames.

Everyone inside the building was able to leave and people rushed to rescue some of its historic paintings.

Culture minister Jakob Engel-Schmidt said 400 years of Danish cultural heritage had gone up in flames.

The building, dating back to 1625, is a stone's throw from Denmark's parliament, the Folketing, and the royal palace, Christiansborg. Danish media said the nearby square was being evacuated.

The old stock exchange was being renovated and had been shrouded in scaffolding and protective plastic covering. It currently houses the Danish Chamber of Commerce, which described the scenes on Tuesday morning as a terrible sight.

Local craftsman Henrik Grage told Danish TV that it was a tragic day.

"This is our Notre-Dame," he said, comparing it with the fire that engulfed the roof and spire of the cathedral in the centre of Paris in 2019.

The Paris fire broke out under the eaves of Notre-Dame on 15 April when it was also shrouded in scaffolding as part of extensive renovations.

Investigators have blamed either a short circuit in the electrics or a worker's cigarette butt that was not properly put out.

The cause of the fire in Copenhagen is also for the moment unknown but emergency services said the scaffolding made their operation more difficult. Much of the building is thought to have been badly damaged by the fire, which officials say was most intense around its tower.

Passing residents joined emergency services, as well as chamber of commerce director Brian Mikkelsen, in saving the art treasures from the Børsen.

Local museum inspector Benjamin Asmussen told Denmark's TV2 that the fire was difficult to watch as the old stock exchange was filled with paintings of Danes who had played important roles since the 17th Century.

The Dutch Renaissance-style building on the city's Slotsholmen, or palace island, was commissioned by Denmark's King Christian IV with the aim of turning Copenhagen into a major trading centre.

Its spire featured four dragons whose tails were twisted into a spear and three crowns, symbolising close ties with neighbours Norway and Sweden.