Among the four, one is a woman and three are men who opened fire at two separate mosques.
Local police have also found and neutralised a number of improvised explosive devices (IEDs) attached to vehicles.
The mass shooting killed 49 people. The country's Prime Minister Jacinda Ardern said: "This is one of New Zealand's darkest days. My thoughts are with Christchurch".
"It is an unprecedented violence in New Zealand.
There is no place for such extreme violence in New Zealand." -