An armed man has been arrested in central Sydney after stabbing a woman and being detained on the street by members of the public, authorities say.
A second woman has been found dead inside an apartment building on the same street but it is unclear whether this is connected to the incident.
Police said the man attempted to carry out further stabbings and there were “multiple crime scenes”.
Video footage shows the suspect shouting “Allahu Akbar” and “shoot me”.
He jumps on a car wielding a knife as another man confronts him with a wicker chair.
The incident unfolded at about 14:00 local time (04:00 GMT) on Tuesday near Clarence St and King St, a busy area in the city centre.
The injured woman was taken to hospital in a stable condition. Police said there was no ongoing threat.
They said they were investigating whether the body found in the apartment was linked to the incident.
Australian Prime Minister Scott Morrison tweeted that the “violent attack” was “deeply concerning”.
The motivation for the attack is not yet known, said Supt Gavin Wood of New South Wales Police.
“It would appear at this stage it is unprovoked, but we are keeping a very open mind as we move forward,” he said.
One witness said she saw the man jump on a car before he was confronted by people on the street who tried to fight him with chairs and pipes.
“The guy had blood on his shirt. He was screaming, holding a knife on his hand, and running up a car just in front of us,” Japanese tourist Aya Yamada told the BBC.
“Another guy with a chair and some fire fighters were chasing him. I was in the car with my husband and friends, and could run away immediately.”
Videos posted online show a man running through the streets brandishing a knife, before people attempt to stop him and eventually tackle him to the ground.
Other images show the suspect being pinned down with a chair and a milk crate, then being taken away by police.
Supt Wood praised those who had intervened in the “extremely dangerous and hostile” situation, saying their actions had helped capture the man.
“They were significantly brave people,” Supt Wood said.
Three British men were among those who helped take the man down, according to the Sydney Morning Herald reported.
Lee Cuthbert, Paul O’Shaughnessy and Luke O’Shaughnessy, all from Manchester, were working nearby when they heard the commotion outside and ran out to help.
“You don’t think, you just kind of react really, it was surreal, very, very surreal,” said Mr Cuthbert.
“We all kind of chased, worked together, but it was Luke who was the real hero. He pursued him the hardest and managed to get a grip of him.”
Authorities urged people to avoid the area. Police said they would release more information as it became available.