At least two people are reported to have been killed in the incident, and others are injured.
What we know
- A vehicle has been driven into a street full of pedestrians in Stockholm, police say.
- At least two people are reported to have been killed, and a large number of people are wounded.
- The incident happened on Drottninggatan, one of the Swedish capital's busy shopping streets.
- Police have stormed Stockholm Central Station, according to CNN partner Expressen.
Swedish King cuts state visit to Brazil short
King Carl XVI Gustaf is to return early from a state visit to Brazil, following the attack in Stockholm.
The monarch issued a statement Friday afternoon saying he and the rest of the royal family had learned of the attack "with dismay."
"We are closely following the developments but our thoughts are already now with the victims and their families."
Report: Stockholm cinemas, theaters closed
A number of cultural institutions in Stockholm have been closed in wake of the attack, including SF movie theaters, the House of Culture, the City Theater and the Royal Dramatic Theater, according to CNN partner Expressen.
Vehicles as weapons: An emerging terror tactic
Stockholm has joined a growing list of cities across Europe and around the world in which vehicles have been used as weapons.
In London last month, British man Khalid Masood plowed into pedestrians on the city's Westminster Bridge before driving into the fence at the Houses of Parliament and attacking a police officer. Five people were killed, and dozens wounded.
That attack followed others in Berlin, Nice, Quebec, Jerusalem and Ohio which have left scores dead, and many more injured.
Mayor: London stands with Stockholm
“My thoughts and deepest sympathies are with the victims and the families who have been affected by the horrific attack in Stockholm today," London Mayor Sadiq Khan said in a statement.
“The full details are still emerging, but once again it looks like we have seen a despicable act of terrorism aimed at harming innocent people and attacking our shared values of democracy, freedom, justice and tolerance.
“Londoners know how it feels to suffer from senseless and cowardly terrorism. And I know we share a steely determination with the people of Stockholm that we will never allow terrorists to succeed."
Police chief: We will do everything we can to find attacker
Sweden's National Police Chief Dan Eliasson has told reporters at a press conference that his officers "will do everything we can to find who is behind this attack."
"What do we know?" Eliasson said. "A truck drove into a shop. We have contact with the man who usually drives this truck."
"There are, as you know, many people injured," he added. "We cannot right now confirm how many people have died or are injured."
Anders Thornberg, head of the Security Police, said authorities in Sweden "are not surprised about this incident, because it has happened before in Europe."
"We are also working and prepared for more," Thornberg added.
Eiffel Tower to go dark in solidarity with Stockholm
The Mayor of Paris, Anne Hidalgo, has announced that the Eiffel Tower will go dark at midnight tonight, local time (6 p.m. ET) in tribute to the victims of the Stockholm attack.
Eyewitness: 'It was like he was driving through paper'
The driver in the Stockholm attack “put his foot on the gas and ran through the crowd," eyewitness Veronica Durango tells CNN.
The truck came from Olof Palmes street and drove down to Drottninggatan, she said.
Durango said a woman walking behind her was run over by the truck and knocked five meters backwards.
"It was like he was driving through paper," she said. "It's like it was nothing."
"I can't even believe how a person could do such a thing," she added. "And then he just kept on going. I was in shock."
Durango managed to jump out of harm's way; otherwise, she said, "it would have been me who died."
Report: Stockholm mall evacuated
The Mall of Scandinavia -- Sweden's biggest mall -- was evacuated following the truck attack, according to CNN partner Expressen.
Witness: Downtown Stockholm 'like a war zone'
From journalist James Savage in Stockholm:
People in central Stockholm are being kept inside their offices and people are being told to return home if they live outside the city center. One eyewitness told Savage the scene "looked like a war zone."
Report: Police storm central train station
Police have stormed Stockholm Central Station after evacuating the public, according to CNN partner Expressen.
Breaking News: Sweden is under attack, says PM
Swedish Prime Minister Stefan Lofven says the country is "under attack."
In a message posted on his official Twitter account, Lofven said: "Sweden is under attack. All indications are that it is terrorism. Be careful and listen to police information."