Prime Minister Jacinda Ardern says 40 people have died in the Christchurch shootings.
Ten were killed in Linwood and 30 at the Deans Ave mosque.
Ardern said it was an "unprecedented" situation and described it as a terrorist attack.
She said it was obvious the attacks had been planned for some time.
The National Security Threat Level had been lifted from low to high.
The Defence Force was transporting more police to Christchurch.
Gunmen have opened fire at mosques in Christchurch, with reports of at least 30 people killed. Four people are in custody - three men and one woman.
The Police Commissioner Mike Bush said "there have been some absolute acts of bravery" in the arrests of the four attackers.
A number of IEDs that were attached to vehicles in Christchurch have been defused by the Defence Force.
