"We believe that 40 people have lost their lives in this act of extreme violence", Ardern said. Australian Prime Minister Scott Morrison described the suspected attacker as an "extremist right-wing violent terrorist".
Mr Peneha said he then went into the mosque to try to help.
Worshippers, possibly dead or wounded, lay huddled on the floor of the mosque, the video showed.
An ashen-faced Ardern said she was unable to confirm the number of fatalities, with events still unfolding.
The shooter, who identified himself on Twitter as "Brenton Tarrant" from Grafton, New South Wales, stormed into Masjid Noor Mosque in Christchurch around 1.40pm local time, gunning down dozens while hundreds of worshipers took part in Friday prayer. "We continue to utilize every possible resource to resolve the situation", Bush said, adding that all mosques in the country had been asked to shut their doors.
The person further claimed that the injured Malaysian was still at one of the mosques in Christchurch that gunmen attacked today.
After the harrowing experience, Ardern described the incident as one of the "darkest days" in New Zealand's history.
New Zealand police said they had detained three men and one woman after attacks on two Christchurch mosques, but they have not provided their identities. He said he was not a member of any organisation, but had donated to and interacted with many nationalist groups, though he acted alone and no group ordered the attack.More news: Android Q Beta First Look!
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"Again we are unsure if there are any other locations outside of that area", he said.
Mr Bush also confirmed police had found improvised explosive devices attached to cars which the defence force had worked to neutralise.
The livestream of the terror attack lasted 17 minutes.
A man reacts as he speaks on a mobile phone outside a mosque in central Christchurch, New Zealand.
Bangladesh team escaped from a mosque near Hagley Park where there were active shooters.
The foreign minister of Indonesia, which has the world's biggest Muslim population, condemned the shooting.
A Twitter representative told CNN that it had suspended an account related to the shooting and was working to remove the video of the attack, and Google, which owns YouTube, said it was also working to remove the footage from its site, according to the AP.