At the scene, bloody tyre tracks on Drottninggatan (Queen Street) showed where the truck had passed.
Glen Foran said he avoided the 30-tonne hijacked beer truck which was coming towards him before it ploughed into a group of shoppers, killing four and injuring 15. "I looked out of the store and saw a big truck". It swerved from side to side.
"We are still trying to determine who the attacker was, if the attack was carried by one or more people, and the number of injured". "It hit a pram with a kid in it, demolished it".
According to Radio Sweden, "large parts of central Stockholm are cordoned off, all metro services are canceled [and] the parliament building (Riksdag) and the government headquarters Rosenbad are in lock-down".
'It took a long time for police to get here.
"Had I arrived there one minute later, I would have been run over".
Authorities in Sweden say they have made one arrest after a truck drove into pedestrians on a major shopping and tourist street in Stockholm Friday, causing multiple injuries and fatalities.
"One person has been arrested on suspicion of terrorist crimes through murder", a spokesperson at the prosecutors office said. According to the BBC, authorities have released "a grainy image of a man, who was caught on CCTV and is deemed a person of interest in the case".
Swedish Prime Minister Stefan Lofven has described the crash as a terror attack.
"These kinds of actions will never succeed". "We have said that this may happen, but we had no indication that it could be done now", he explained.
Sweden's King Carl Gustaf said in a statement: "Our thoughts are going out to those that were affected, and to their families".
Police said security at Swedish borders had been heightened. He "may have connections" to the attack, police said, but they provided no details. All subway traffic was halted on police orders.
Photos from the scene show at least three bodies covered in blankets near a pedestrian walkway in the shopping district.
Swedish brewery Spendrups said its truck had been stolen on its way to a restaurant delivery earlier in the day. Smoke rose from the front of the store, located in the upscale Ahlens City retail hub in the heart of Stockholm. It was awful to see'.
"Four people have died and 15 people have been injured", Stockholm police spokesman Lars Bystrom told AFP.
At a restaurant delivery "someone jumped into the driver's cabin and drove off with the auto while the driver unloaded", said communications director Mårten Lyth, according to TT.
The deadliest came a year ago in France on the Bastille Day national holiday when a man rammed a truck into a crowd in the Mediterranean resort of Nice, killing 86 people. Al Qaeda in 2010 urged its followers to use trucks as a weapon.
Another man was arrested in Hjulsta, a working-class neighbourhood of Stockholm, but police refused to confirm a link with the attack.
Is it a terror attack? "And this is a pretty cunning modus operandi", he said.