Four people are in custody after terrorists opened fire at two mosques in Christchurch, New Zealand, killing at least 49 people.

Hundreds of people were inside the Masjid Al Noor and Linwood Masjid Mosques in Hagley Park when at least one gunman started open firing during prayers on Friday afternoon.

Authorities have announced that a total of 49 people have lost their lives and a further 48 people were injured in the attacks.

A total of three men and one woman have been arrested. One man, aged 28, has now been charged with murder and will appear in a Christchurch court tomorrow.

Police Commissioner Mike Bush said of the three other people apprehended, one, who was armed when arrested, may have nothing to do with the incident.

View photos Horrific footage posted to YouTube shows a gunman approach the front doors of the mosque and open fire. More

“With the two others, who were also armed when they were arrested, we are working through what their involvement is,” Commissioner Bush said.

“We have recovered a number of firearms from both of the scenes.”

New Zealand Prime Minister Jacinda Ardern said: “It is clear that this can now only be described as a terrorist attack.”

Witnesses have described seeing bodies laying scattered on the ground and “blood everywhere”, while graphic footage, understood to be a live stream of the shooting, has also been uploaded to YouTube.

It shows a man dressed in a military-style, camouflage outfit, carrying a series of automatic rifles exit his car, walk to the front door of the mosque and open fire.

View photos Ambulance staff rush a man from outside a mosque in central Christchurch. Source: AAP More

Three men and one woman are now in custody, however police have not ruled out there are others involved.

Prime Minister Scott Morrison has confirmed that one of the people arrested is an Australian-born citizen.

Businesses and schools around the city were immediately placed into lockdown, as armed police guarded the streets.

Police are also instructing people to remain indoors, confirming that a bomb has been found in a Subaru near the scene of the first mosque shooting.

The Bangladesh cricket team was also inside the mosque for Friday prayer when the shooting started, however, they were able to escape unharmed.

‘So much blood’: Witnesses describe horror

View photos A man reacts as he speaks on a mobile phone outside the mosque. Source: AAP More

One witness told local media that he had seen three people lying on the ground, bleeding outside the building.

“I heard a big sound of the gun. And a second one, I ran. Lots of people were sitting on the floor. I ran behind the mosque,” he told TVNZ.

“The floor. There’s lots of blood on the floor, you can see when you go in.”

Witness Benjamin Jellie said he ran outside when he heard gunshots.

“I saw people jumping over the back fence of the mosque into Oakward Close. I heard at least 20 [gunshots],” he told the NZ Herald.

View photos A Twitter account believed to belong to the gunman uploaded images of his arsenal before the shooting. More

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