One of the four has already been charged with murder and will appear in court tomorrow but Police Commissioner Bush declined to confirm the name of the suspect prior to the court hearing.
As for the suspects, Ardern said, "these are people who I would describe as having extremist views that have absolutely no place in New Zealand".
Police found multiple firearms at both locations, as well as two improvised explosive devices attached to a vehicle that were going to be detonated as part of the attack.
New Zealand's Prime Minister, Jacinta Arden called the attack "one of New Zealand's darkest days".
The 1 NEWS broadcaster reported, citing an Australian police source, that the shooter was Brenton Tarrant from the city of Grafton in Australia's eastern New South Wales state.
Moreover, Christchurch mayor Lianne Dalziel said she was "shocked beyond words" by the shootings.
"I've been in contact with my Australian colleagues - they have no information on them at all either", he said. "We should pray for the people of New Zealand, but especially communities around Christchurch that have suffered so much in recent years".
A man in his late 20s has been charged with murder, and two others arrested at the scene are being investigated.More news: Hammond could have ended austerity earlier without Brexit
More news: Chiefs release veteran safety Eric Berry
More news: National Football League draft prep: Biggest takeaways from Kyler Murray's pro day
The Pittsburgh synagogue attack prompted an outpouring of interfaith solidarity between Muslims and Jews at the time, with the SAJBD statement - one of several from Jewish organisations so far - showing that the Queensland mosque attack has inspired the same.
"Feeling very sick, that person is brainless and a savage", said one Indonesian twitter user who identified himself as Farhan Adhitama. He then replies: "Just a ordinary White man, 28 years old".
Their attacks left 49 people dead and at least 48 injured.
Turkey's President Recep Tayyip Erdogan condemned the deadly attack on two mosques in New Zealand, saying it illustrated the growing hostility towards Islam "idly" watched by the world.
Police were still treating the incident as ongoing into Friday evening local time and urged Christchurch residents to stay indoors and monitor the police website and social media.
Chicago police said there are no known threats to Chicago, but they will be keeping a closer eye on mosques.
We were not chosen for this act of violence because we condone racism, because we are an enclave for extremism.
"We are in contact with federal partners and the global intelligence community monitoring the tragedy in New Zealand", CPD spokesman Anthony Guglielmi said.
The Turkish leader, who often criticises Islamophobic attitudes, called for the West to act to prevent similar attacks. It's also requesting extra police patrols at their mosque in Old Irving Park, their education center in Morton Grove, and their campus in Skokie.