Forty people have been killed and more than 20 seriously wounded in shootings at two mosques in Christchurch.
Witnesses told media that a man dressed in a military-style, camouflage outfit, and carrying an automatic rifle had started randomly shooting people in the Al Noor mosque.
The Bangladesh cricket team was arriving for prayers at the mosque when the shooting occurred but all members were safe, a team coach told Reuters.
Three men and one woman are in custody, police commissioner Mike Bush said, but warned more suspects may be at large.
Police advised people to stay away from mosques.
Police are aware there is extremely distressing footage relating to the incident in Christchurch circulating online. We would strongly urge that the link not be shared. We are working to have any footage removed.- New Zealand Police (@nzpolice) 15 March 2019
Prime Minister Jacinda Ardern said there was no place in New Zealand for such acts of extreme violence.
Police said earlier they were hunting "an active shooter" in the centre of Christchurch city.
"A serious and evolving situation is occurring in Christchurch with an active shooter," New Zealand Police Commissioner Mike Bush said.
"Police are responding with its full capability to manage the situation, but the risk environment remains extremely high."
Media reported that a gunman opened fire inside mosque in Christchurch's Hagley Park district. There were reports of armed police at a second mosque in the suburb of Linwood.
Radio New Zealand quoted a witness inside the mosque saying he heard shots fired and at least four people were lying on the ground and "there was blood everywhere".
"Horrified to hear of Christchurch mosque shootings. There is never a justification for that sort of hatred," said Amy Adams, a member of parliament from Christchurch.
The Bangladesh cricket team is in Christchurch to play New Zealand in a third cricket test starting on Saturday.
"They were on the bus, which was just pulling up to the mosque when the shooting begun," Mario Villavarayen, strength and conditioning coach of the Bangladesh cricket team, told Reuters in a message.
"They are shaken but good."
Dressed in black
Witness Len Peneha said he saw a man dressed in black enter the Masjid Al Noor mosque and then heard dozens of shots, followed by people running from the mosque in terror.
He said he also saw the gunman flee before emergency services arrived.
Mr Peneha said he went into the mosque to try and help: "I saw dead people everywhere."
"There were three in the hallway, at the door leading into the mosque, and people inside the mosque," he said.
"I don't understand how anyone could do this to these people, to anyone. It's ridiculous."
Suddenly the shooting began
A man who was present during one of the incidents spoke to local news channel TVNZ: "It was very peaceful, calm and quiet, as it is when the sermon starts, you could hear a pin drop.
"Then suddenly the shooting started. It started in the main room... I was in the side room, so I didn't see who was shooting but I saw that some people were running out to my room where I was in, I saw some people had blood on their body and some people were limping. It was at the moment I realised things were really serious," he added.
"So I tried too get out and I pushed myself at the back where my car was, and from there I heard the shooting, it went on six minutes or more, I could hear screaming and crying, I saw some people drop dead, some people were running away, I was in a wheelchair, so I couldn't get anywhere.
"He did his massacre inside the mosque."
Muslims account for just over one percent of New Zealand's population, a 2013 census showed.