This afternoon in Melbourne, Australia, a man stabbed three people, leaving one dead, in an incident that is being treated as a terror attack.
Police were called to the scene in Bourke Street, initially responding to a vehicle which had been set on fire.
When two officers arrived they were confronted by an attacker wielding a knife, who was eventually shot dead.
The chief commissioner of Victoria Police, Graham Ashton, has confirmed that counter-terrorism police have launched an investigation.
Footage of the distressing incident has been shared online of the heroic attempts to subdue the attacker by bystanders.
One person is seen brandishing a chair, while another grabs a shopping trolley to push at the man, falling down in the process.
The man then makes a second attempt to push the trolley at the attacker, and then a third as police manage to chase him up the street.
Warning: The following video may contain footage that some may find distressing.
Although this is an incredibly serious incident, people have taken some levity in the heroic efforts of the man with the trolley and have been championing him on social media.
Elsewhere, people are trying to discover the identity of the man to congratulate him in person.
Daniel Andrews, the premier of Victoria, paid tribute to those that acted so valiantly in their attempts to protect their city.