One person is in custody, Police Commissioner Mike Bush said, but it is not know if other gunmen are still on the loose.
A person appearing to be a white supremacist issued a warning on social media ahead of the attack and appears to have streamed live video of at least one of the shootings taking place.
Parts of central Christchurch, including schools, are in lockdown after the incidents.
Eyewitnesses said as many as 15 people may been hit at one mosque, the Masjid Al Noor mosque on Deans Ave.
One eyewitness told 1 News a gunman came in the front door of the mosque. "Everybody just ran to the back door to save themselves," he said.
They hid under cars while the firing continued. Some people then jumped a fence to escape and hid in a nearby house.
There was also another shooting at mosque in Linwood Ave.
Multiple people have been seen arriving on stretchers at Christchurch Hospital, including children.
Some reports say an automatic weapon was used and there were many shots fired.
Another eyewitness Mohammed Nazir told 1 News that he saw the gunman come into the mosque and he saw people injured on the floor, including two women.
He said there was lots of blood on the floor.
Police have put in cordons shutting down areas of the city, and schools in the area are in lockdown.
They asked people to keep out of the area in Christchurch and to stay away from all mosques in New Zealand today.