According to initial reports, the Bangladesh cricket team was inside one of the mosques, but all managed to escape.
Speaking after the attack the Bangladeshi cricket coach Mario Villavarayen said the players heard shots being fired when they fled the mosque.
All schools in Christchurch have been placed on lockdown, police commissioner Mike Bush said.
Gunfire was heard coming from the direction of the mosque and several people were seen on the ground outside the building, One News reported.
Christchurch City council said in a statement: "In response to a serious ongoing incident we're locking down number of central city buildings, including the Civic Offices and Central Library".
People in central Christchurch have been urged to stay indoors and report any suspicious behaviour immediately to authorities.
An eyewitness inside the mosque says he heard shots fired and says at four people were lying on the ground and "there was blood everywhere".More news: WWE Fastlane Results, Rumors On Road To Wrestlemania
Bangladesh's performance and strategic analyst Shrinivas tweeted about the escape. They ran back through Hagley Park back to the Oval.
Christchurch resident Katherine Jamieson is in lockdown in her home, which is located down the road from the Mosque.
Radio Sport commentator Bryan Waddle, who is at the Hagley Oval, very close to the Al Noor mosque, is reporting that staff at the stadium have told them to remain where they are after "a new incident".
New Zealand Prime Minister Jacinda Ardern described the incident as an "unprecedented act of violence".
"Police believe there may be other offenders", the New Zealand Police tweeted.
"I spoke to one of them shortly after (the incident)".
A man in the mosque at the time, who would not give his name, said there were "bodies all over me". "Frightening experience and please keep us in your prayers", he wrote.
Ibrahim said people began running out of the mosque and he "had to jump out of the wall" to escape.