[WATCH] Updated | 49 killed in New Zealand after gunmen attack mosques

Gunmen entered two mosques and began shooting in New Zealand's city of Christchurch on Friday killing 49 people, an unprecedented attack in the quiet country in the Pacific.  

New Zealand's Prime Minister Jacinda Ardern told a news conference that 20 others were in serious condition after the "terrorist" attack. 

Police Commissioner Mike Bush said four suspects were in custody, three men and a woman.

Bush said a number of firearms had been recovered from both shooting sites, and explosive devices were found in a car belonging to one of the suspects.

Ardern said, "This is, and will be, one of New Zealand's darkest days."

Authorities have not described the scale of Friday's shootings but urged people in central Christchurch to stay indoors. It advised all mosques in the city to shut down until further notice. Armed police were also seen at Papanui High School in Christchurch, which was cordoned off.

Police warned worshippers not to visit mosques "anywhere in New Zealand". A lockdown imposed throughout Christchurch was called off at about 5:00 am GMT. 

Australian Prime Minister Scott Morrison said one of the suspects was an Australian national, calling him an "extremist, right-wing, violent terrorist". 

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.

Peneha, who lives next to the mosque, said he went into the building to try and help. "I saw dead people everywhere."

One man in the mosque, with blood stains all over his clothes, said he hid under a bench as the shooting took place. He said about 50 people were inside the building. 

Clarke said some worshippers managed to escape through windows and doors but "many people had been hit, some as young as 16".  

About 10 to 15 people were seen outside the mosque, "some alive, some dead", he said. 

"It was unbelievable. I saw about 20 people, some dead, some screaming," one eyewitness told local television.

"I saw on the floor so many bullet shells, hundreds. I saw one guy trying to run out, and he was shot dead."

One of the gunmen shared a live stream of the attack on Facebook and posted content on Instagram. Facebook said it has taken down the video and was removing praise for the gunman.

"Police are aware there is extremely distressing footage relating to the incident in Christchurch circulating online," a police statement said. "We would strongly urge that the link not be shared. We are working to have any footage removed."

There were reports racist literature was left behind at the scene denouncing "invaders".

Commissioner Bush said local police officers apprehended the four suspects. "There's been some absolute acts of bravery," he said without elaborating.  

"I won't assume there aren't others but I don't have any information to that effect," Bush told a press conference.

He said a number of bombs were detected and neutralised on the attackers' automobiles.

"There were a few reports of IEDs strapped to vehicles which we were able to secure," he said, referring to improved explosive devices. 

Asked by reporters whether police considered Friday's carnage a "terrorist attack", Bush said an investigation was under way. 

ESPN Cricinfo reporter Mohammed Isam said members of the Bangladesh cricket team, who are set to play a test match in Christchurch on Saturday, escaped from the mosque.

Mario Villavarayen, strength and conditioning coach of the Bangladesh cricket team, was quoted by the New Zealand Herald as saying the team was close to where the shooting occurred, but was safe.

"The players are shaken up but fine," Villavarayen was quoted as saying.

Peneha described the scene at Masjid Al Noor as " unbelievable".

"I don't understand how anyone could do this to these people, to anyone. It's ridiculous. I've lived next door to this mosque for about five years and the people are great, they're very friendly. I just don't understand it," he said.

Muslims account for just 1% of New Zealand's population, a 2013 census showed.

"Many of those who would have been affected by this shooting may be migrants to New Zealand," Ardern said.

"They may even be refugees here. They have chosen to make New Zealand their home and it is their home ... they are us. The persons who perpetuated this violence against us ... have no place in New Zealand."

Mass shootings in New Zealand are exceedingly rare. The deadliest in modern history occurred in the small town of Aramoana in 1990, when gunman David Gray shot and killed 13 people following a dispute with a neighbour.

New Zealand shooter pencilled Malta on his gun barrel

One of the attackers of the New Zealand massacre inscribed 'Malta' on his weapons twice: once on the barrel of his shotgun and another time on the foregrip of his assault rifle.

The shotgun inscription specifically said 'Malta 1565' in reference to the Great Siege of Malta. The foregrip inscription read 'Malta 1571' in reference to the Battle of Lepanto, when Malta sailed out to seek a 250-galley Muslim fleet at Lepanto, Italy.

The Australian-born shooter had even published a 40-page manifesto on image-board website 8chan. Malta was not invoked in the shooter's manifesto but Islamophobic and white supremacist rhetoric riddles the pages. Most of the writings appear to be nonsensical however.

The guns used by Tarrant (he had at least six in his car) were covered in racial slurs like 'Kebab Remover' and 'Migration Compact.' Another scribbling reads: ‘Vienna 1683’ – a reference to the Battle of Vienna – another historic clash between Christian and Ottoman forces.