The European Union and countries across the continent offered Sweden support and solidarity today following what the Swedish government said appeared to be a terrorist attack using a vehicle in central Stockholm.

"An attack on any of our member states is an attack on us all," said President of the European Commission, Jean-Claude Juncker. "One of Europe's most vibrant and colourful cities appears to have been struck by those wishing it – and our very way of life – harm.

"We stand shoulder to shoulder in solidarity with the people of Sweden and the Swedish authorities can count on the European Commission to support them in any which way we can."

"My heart is in Stockholm this afternoon," President of the European Council Donald Tusk tweeted. "My thoughts are with the victims, and their families and friends, of today's terrible attack."

German government spokesman Steffen Seibert also reacted to the news.

"Our thoughts are with the people in Stockholm, the injured, relatives, rescuers and police. We stand together against terror," he said in a tweet.

The French government said President Francois Hollande expressed his horror and outrage at the attack.

"France expresses its sympathy and solidarity with the families of the victims and all Swedes," the Elysee Palace said in a statement.

Sweden's Nordic neighbours also expressed their horror.

"Terrible news from Stockholm. Our thoughts are with our neighbours and friends in Sweden," Finland's Prime Minister Juha Sipila wrote in Swedish on his Twitter account.

Danish Foreign Minister Anders Samuelsen, speaking in Vienna, expressed his sadness and called for more cooperation between countries to combat attacks.

"It's so horrible to learn about this terror attack ... It's horrible, it's disgusting and we have to fight this terror appearing in Europe," he said.

"And one thing we can do is to cooperate even closer on exchanging data, exchanging information about what we learn of those terror cells or terrorists," Samuelsen added.

"Terrible event in Stockholm," Norwegian Finance Minister Siv Jensen tweeted.