- 3 people have been killed in the truck attack; 15 wounded, 9 of them seriously, according to The Associated Press.
- All subway traffic has been shut down in Stockholm.
- Swedish police are leading the investigation and working with Swedish security service, treating the incident as a possible terror attack.
- One suspect has been arrested, according to Reuters.
Police launched a manhunt in Sweden's capital Friday for a suspect who rammed a truck into a department store in a likely act of terrorism — killing at least two people and injuring many others, officials said.
The vehicle plowed into a crowd on Stockholm's busy street of Drottninggatan before barreling into the side of the Ahlens store, the country's security agency said. Panicked pedestrians and shoppers were caught scrambling for safety.
During a news conference, police described the suspect as a man in a green jacket and hoodie with a mustache and beard.
"Everything indicates that this is a terrorist act," Swedish Prime Minister Stefan Löfven said.
By mid-afternoon, Swedish police said one person had been arrested in relation to the attack, according to a local news station. Police were also investigating the truck and said they were in contact with its owner.
Spectators took to social media shortly afterwards to post what they were witnessing.
Friday's incident marks the latest in a series of low-tech, vehicle-based terror attacks across Europe over recent years.
Löfven told reporters that at least two people had been killed and the security service said there were a "large number" of injuries.
Swedish broadcaster SVT said shots had been fired — although officials would not confirm that detail.
Eyewitnesses described confusion as smoke from the crash filled the building. Maria Nathalie said she was in the department store at the time of the incident.
"People started running down the stairs when the fire alarm started," she told NBC News. "And when we came down to the bottom of the building, all we could see was a lot of smoke and there was someone who helped us get out on the other side of the building."
John Backvid, a 25-year-old Stockholm resident and local university student, said he had just gotten out of the subway across the street from the department store when the crash occurred. He could smell smoke and came across a chaotic scene.
"I looked up and saw people running towards me and I saw the truck on the other side," Backvid said.
People were worried that a hot dog vendor's gas grill might spark an explosion, and Backvid said he and others started running. He also noticed someone performing CPR on a victim.
The incident comes two weeks after a man rammed a car through crowds in London and killed four civilians before stabbing to death a police officer.
Some residents in Sweden said they would not let a terror-related scare paralyze them.
"We need to stand up and continue our lives and show that we are not afraid," Backvid said.
—CNBC's Lauren Thomas, Reuters and The Associated Press contributed to this report.