Mr Mazharuddin said one of his friends had died at the scene and another was bleeding heavily as he tried to contact emergency services.
Meanwhile, cities around the USA are boosting security at mosques ahead of Friday's prayer services.
Authorities said none of the suspects had been on any watch list. More than 200 people were injured. Police have yet to confirm the identity of the shooter, while 4 people are in custody.
Ardern said her country is treating the shootings as a "terrorist incident".
What else do we know about the attack?
Four people have been detained, and one is Australian.
'BLOOD EVERYWHERE' After parking his vehicle he took two guns and walked a short distance to the entrance of the mosque.
Two mosques, the Deans Ave. mosque and the Al Noor mosque, were the targeted locations.
Syed Mazharuddin was praying at the Linwood mosque in Christchurch on Friday around lunchtime when a man wearing protective gear entered and began shooting at men, women and children inside.
The New Zealand-Bangladesh third Test match set to be played in Christchurch was axed.
"It is such a sad and devastating reminder of the evil that can be ever present about us", Morrison said of the attacks. "There is never a justification for that sort of hatred", said Amy Adams, a member of parliament from Christchurch.
Muslims make up only one percent of New Zealand's population.
The Indonesian Embassy in Wellington sent a team to Christchurch that is coordinating with New Zealand officials.
It said it strongly condemns the attack.
Police Commissioner Mike Bush said: "A serious and evolving situation is occurring in Christchurch with an active shooter".
"Of the 40 people who have been treated at Christchurch Hospital, one has now passed". "It is clear this is one of New Zealand's darkest days".
When asked if police were looking for any other persons of interest related to the case, Bush responded that "we never assume that there aren't other people involved" but that "at this point we are not looking for any other persons". I acknowledge that that may mean that some families are separated, but please continue to listen out for information as it comes to light that's been directly provided by the New Zealand Police with further information. The 74-page manifesto claimed that the European population was being displaced in their homelands by immigrant groups with higher birth rates. "There were three in the hallway, at the door leading into the mosque, and people inside the mosque", Peneha said.
"Police said there were multiple fatalities and one person was in custody, but no details were immediately available".
"They may even be refugees here".
News reports characterized the mosque shootings as the deadliest incident in New Zealand's history.
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