Police have confirmed they responded to a call, and television outlets in New Zealand and Australia have extensively reported on the shooting over the last hour.
"A serious and evolving situation is occurring in Christchurch with an active shooter", Police Commissioner Mike Bush was quoted as telling reporters.
Police have not yet described the scale of the shooting, but urged people in central Christchurch to stay indoors.
New Zealand's Prime Minister is expected to speak shortly.More news: Champions League - quarter-final draw details
Amid the chaos, the players reportedly told locals walking towards the mosque to turn around and avoid the scene.
Armed police patrol outside a mosque in central Christchurch, New Zealand, Friday, March 15, 2019.
A witness has said that the shooter was dressed in military gear and had a high-powered rifle.
It is understood members of the touring Bangladesh cricket team were in the mosque when the shooting occurred but they are believed to be safe.
"Several minutes after they were barred from getting off the bus, the players escaped and ran through Hagley Park", Isam wrote.More news: Shares - Boeing Weighs on Dow As Gross sales Knowledge Carry S&P, Nasdaq
The Bangladesh team were able to return to Hagley Oval, where Saturday's third Test was scheduled to take place.
An eyewitness told Radio New Zealand he heard shots fired and four people were lying on the ground, with "blood everywhere".
A witness who has inside the mosque told ABC News that it was very "peaceful, calm and quiet" when the shooting started.
Armed police patrol outside a mosque in central Christchurch.
"When I heard that there is a shooting - the sound whats coming".More news: Callum Hudson-Odoi reveals Chelsea FC’s best player in training
"I've lived next door to this mosque for about five years and the people are great, they're very friendly", he said. And a second one, I ran.