She announced that New Zealand had raised its security threat level to the highest degree and said four suspects who harbored extremist views were now in police custody with one man who police said was in his late 20s charged with murder.
New Zealand's Prime Minister Jacinda Ardern held a press conference following the shooting at the two mosques in Christchurch, saying the incident marked "one of New Zealand's darkest days".
He said: "There can be no justification for acts of violence and discrimination based on religion or beliefs".
In the video live-streamed by Tarrant, a man inside a mosque appears to say "Welcome brother" as a gunman approaches.
The death toll from attacks on two mosques of New Zealand's Christchurch rose to 49 and 48 others were wounded, New Zealand Police Commissioner Mike Bush said on Friday.
"All of us, of whatever religious tradition, can identify with what that might mean for a congregation gathered for worship", he said.More news: Gambino 'mob boss' shot dead outside NY home
Two explosive devices attached to cars have also been decommissioned by police.
Asked about the attackers not being on intelligence agency watchlists, Ms Ardern said it was an indication that they "had not acted in a way that warranted it".
In full, Her Majesty said: "I have been deeply saddened by the appalling events in Christchurch today".
"I imagine that these would have represented particular brothers, fathers, sons".
Kate was presenting the news programme alongside Charlotte Hawkins, and they were reporting the attack together. This is not an enclave for that kind of behaviour, for that kind of ideology.
"I am not going to let this change New Zealand's profile, none of us should".More news: British ex-soldier to be charged in Bloody Sunday killings
Speaking about her family, she said: "I'm sure many of you at home will have relatives in New Zealand and it will be very alarming for you".
"I know our communities will be thinking of those who have lost their lives and that they will pray for those who have been lost; their grieving families and for those who have been injured".
Officers responded to reports of shots fired in central Christchurch at about 1.40pm local time (12.40am GMT), and urged people in the area to stay indoors.
"They have chosen to make New Zealand their home, and it is there home".
Tamim Iqbal tweeted: "Entire team got saved from active shooters!"
The video footage has been posted after New Zealand Police explicitly urged people to not share the "extremely distressing footage relating to the incident in Christchurch circulating online".More news: Google is going all-in on the squircle icon for the Play Store
In a statement issued by Áras an Uachtaráin the President said that the attacks have "appalled people all over the world". "This has been done deliberately to also demonise legitimate Muslim political struggles", he tweeted.