Here is what we know so far about the attacks:
During afternoon prayers on Friday -- Islam's holy day -- a gunman opened fire inside the Masjid al Noor mosque in central Christchurch, killing forty-one. Another seven were slain at a second mosque five kilometres away in suburban Linwood, three of them outside the building. It is unclear where the remaining victim died.
Witnesses said some victims were shot at close range, with a Palestinian man at one of the mosques saying he saw someone shot in the head.
He described shots fired in quick succession and scenes of panic as people started running out "covered in blood".
Another said he saw his wife lying dead outside as he escaped, with one more saying he witnessed children being shot.
What was the police response?
Police imposed a city-wide lockdown, sending armed officers to a number of scenes, and two IEDs (improvised explosive devices) were found attached to a vehicle and neutralised.
Three men and a woman were detained. One of the men was later charged with murder, and two others remained in custody, though their role in the attacks was not clear.
Police warned Muslims not to visit mosques "anywhere in New Zealand", a country of nearly five million where mass shootings are rare.
Amid heightened tensions, the military carried out controlled explosions on two bags left unattended in central Auckland, although they turned out not to be suspicious.
Christchurch city council offered a helpline for parents looking for kids attending a mass climate change rally nearby.
New Zealand police also evacuated residents living near a property in the city of Dunedin, some 350 kilometres (220 miles) from Christchurch, that they believe is linked to the attacks.
Who were the victims?
A Jordanian man was killed in the attack, the country's foreign ministry said, the first and only victim identified so far.
People from around the world were in the mosque at the time of the assault.
Among them were were six Indonesians -- three of whom were reported safe, the country's foreign minister Retno Marsudi said, adding they were searching for the others.
A Saudi Arabian man, two Malaysians, two Turks and at least five Jordanians were among those wounded.
India's high commissioner to New Zealand said nine people of Indian nationality or origin were missing.
Young children were among 48 people being treated at Christchurch Hospital.
Some narrowly escaped the carnage, including the Bangladesh cricket team who arrived at the Masjid al Noor mosque minutes after the shooting began.
Manager Khaled Mashud said the team saw "bloodied people coming out of the mosque... we kept our heads down in the bus in case of any firing".
What is known about the attacker?
He has not been officially named, but Australian Prime Minister Scott Morrison said he was an Australian citizen, and described him as "an extremist, right-wing, violent terrorist".
He published a racist manifesto on Twitter before the shooting then livestreamed his rampage on Facebook.
Entitled "The Great Replacement", the 74-page manifesto said the gunman -- who identified himself as an Australia-born, 28-year-old white male from a low-income, working-class family -- had wanted to attack Muslims.
The gunman also said he had travelled for several years, visiting France, Spain and Portugal, but Australian media reported before going to New Zealand he had been a personal fitness trainer in the town of Grafton north of Sydney.
The title of the manifesto has the same name as a conspiracy theory originating in France that believes European populations are being displaced in their homelands by immigrant groups with higher birth rates.
A number of pictures were posted to a social media account of a semi-automatic weapon covered in the names of historical figures, many of whom were involved in the killing of Muslims.