The massacre by at least one gunman during Friday prayers in the city of Christchurch is the country’s worst ever mass shooting and was condemned throughout Asia.

New Zealand’s police commissioner said on Friday 49 people were killed in Christchurch at two mosques and one man of four people arrested had been charged with murder.

As many as 41 people died at one mosque, seven at another and one person died in hospital, Mike Bush told reporters, describing the attack as a ‘very well-planned event’.

The man charged with murder is in his late 20s and should appear in Christchurch court on Saturday, Bush added.

Ardern said New Zealand had been placed on its highest security threat level. She said four people in police custody held extremist views, but had not been on any police watchlists.

Video footage widely circulated on social media, apparently taken by a gunman and posted online live as the attack unfolded, showed him driving to one mosque, entering it and shooting randomly at people inside.

Worshippers, possibly dead or wounded, lay huddled on the floor of the mosque, the video showed. Reuters was unable to confirm the authenticity of the footage.

One man who said he was at the Al Noor mosque told media the gunman was white, blond and wearing a helmet and a bulletproof vest. The man burst into the mosque as worshippers were kneeling for prayers.

‘He had a big gun ... he came and started shooting everyone in the mosque, everywhere,’ said the man, Ahmad Al-Mahmoud. He said he and others escaped by breaking through a glass door.

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’.

Ardern said 30 people were killed at the Al Noor mosque, the city’s main mosque, and another 10 at a mosque in the suburb of Linwood.

‘This is one of New Zealand’s darkest days,’ she said.

New Zealand’s police commissioner Mike Bush said four people - three men and a woman - had been taken into custody.

Australian prime minister Scott Morrison said one of the men in custody was Australian.

Police said IEDs, improvised explosive devices, were found with a vehicle they stopped.

The online video footage, which appeared to have been captured on a camera strapped to the gunman’s head, showed red petrol canisters in the back of his car, along with weapons.

All mosques in New Zealand had been asked to shut their doors, police said.

The Bangladesh cricket team was arriving for Friday prayers when the shooting occurred but all members were safe, a team coach told Reuters.

Political and Islamic leaders across Asia expressed their disgust at the deadly shooting.

‘Indonesia strongly condemns this shooting act, especially at a place of worship while a Friday prayer was ongoing,’ foreign minister Retno Marsudi said in a statement.