Facebook has activated its Safety Check feature in the wake of a suspected terror attack in Sweden.
At least three people have been killed after a lorry drove into crowds in Drottninggatan, a shopping district in Stockholm.
The feature is designed to allow Facebook users in the area to quickly reassure friends and family members that they're not in danger.
Users can also share the Safety Check on their own timeline or that of a friend, as well as in a group, page, event and private message.
Facebook activates the feature whenever a certain number of people in an affected area post an update about the incident.
“I went to the main street when a big truck came out of nowhere," a witness told Swedish daily paper Aftonbladet.
"I could not see if anyone was driving it but it got out of control. I saw at least two being run over. I ran as fast as I could from there.”
Swedish police have issued a warning to the public to avoid Stockholm city centre.
Aftonbladet is reporting that police were ordering people to leave the scene in the immediate aftermath of the incident saying, "Warning – terror attack".