Multiple people have been killed after a gunman opened fire at two mosques in the New Zealand city of Christchurch.
Police have taken one person into custody after the gunman shot at worshippers as they gathered for Friday prayers.
"We have one person in custody, but we are unsure if there are other people," police chief Mike Bush said.
"We are dealing with a very serious and tragic series of events in the Christchurch-Canterbury area ... They involve an active shooter. They involve multiple fatalities."
People had been killed at two separate mosques, he said, urging everyone across the country to avoid mosques.
Armed police were deployed around the Masjid Al Noor mosque where shooting broke out at 1.40pm (NZT) on Friday, with the city's schools and hospital locked down.
Reports later emerged of shots at another mosque in Linwood Avenue.
Prime Minister Jacinda Ardern described it as one of New Zealand's darkest days.
"I would describe it as an unprecedented act of violence, an act that has absolutely no place in New Zealand, " she said.
A witness, with blood splatters across his shirt, told AAP the shooter changed magazines seven times after opening fire as the crowd gathered to pray.
"When the shooting started people started rushing out, and the door was closed, and the guys came on them and started shooting them," he said, describing how he hid under a bench and pretended to stop breathing.
"He went to all the different [rooms] and he shot everyone."
Several hundred people were inside and witnesses reported seeing "blood everywhere", according to Radio New Zealand.
Witnesses described seeing as many as 40 people injured.
"I heard a big sound of the gun. And a second one, I ran. Lots of people were sitting on the floor. I ran behind the mosque," one told TVNZ.
"The floor. There's lots of blood on the floor, you can see when you go in."
An unverified video that appeared to show a shooting, taken from a helmet camera, had been posted online.
Christchurch residents have been told to remain indoors and report suspicious behaviour.
The Bangladesh cricket team, in Christchurch to play New Zealand on Saturday were in the vicinity, and had been left shaken but uninjured, their coach told media.
Australian diplomats in New Zealand are seeking information on whether any citizens were affected.
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