Police did not immediately comment on whether the incident took place in the mosque or nearby.
Local media said there were multiple casualties at one mosque and said another had been evacuated, and there were reports that members of the Bangladesh cricket team were also present at one site.
A reporter following the Bangladesh cricket team, who are now in New Zealand, tweeted that that had "escaped from a mosque near Hagley Park where there were active shooters". They didn't see anything but heard gunshots.
Much of the coaching staff were back in the team hotel while the head coach Steve Rhodes was at the ground.
It is understood that the team was on a bus after it had gone to the mosque situated near Hagley Oval where Bangladesh and New Zealand were scheduled to play a One Day International on Saturday.More news: Murdoch's News Corp wants Google split up in Australia
A spokeswoman did not know how many patients were expected, adding it was an "evolving situation".
Several hundred people were inside the mosque at the time and witnesses reported seeing at least four people on the ground and "blood everywhere", according to Radio New Zealand.
"Entire team got saved from active shooters", Iqbal tweeted.
"It was very traumatic there and people were running out from that mosque presumably, and the Bangladesh players were coming out".
"I heard a big sound of the gun".More news: Democrat rising star O'Rourke announces 2020 White House bid
"When that was happening, one of the players had called me to contact the police". Lots of people were sitting on the floor. "I ran behind the mosque", he told TVNZ.
"The floor. There's lots of blood on the floor, you can see when you go in".
In response to "a serious ongoing firearms incident", police said all schools have been placed in lock-down.
A mass casualty plan has been activated in the greater Canterbury region, which includes the city of Christchurch.More news: Woman awarded $42 million in baby powder terminal cancer lawsuit