Forty people have been killed and at least 20 others injured in shootings at two mosques in New Zealand city of Christchurch in an unprecedented attack in the quiet country in the Pacific.

New Zealand's Prime Minister Jacinda Ardern told a news conference that the mosque shootings appear to have been a well-planned "terrorist attack".

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

The prime minister also said two explosive devices attached to suspect vehicles were found and have been disarmed.

The two known targets were the Masjid Al Noor in central Christchurch, and a second mosque in suburban Linwood.

Sam Clarke, a reporter with TVNZ, spoke with several people inside the Masjid Al Noor mosque when the shooting began. He told Al Jazeera a man entered with an automatic weapon and began firing.

"A gunman - dressed in black with a helmet carrying a machine gun - came into the back of the mosque and started firing into the people praying there," said Clarke. It was later confirmed that 30 worshippers were killed at the mosque, including women and children.

Police also confirmed that 10 people have been killed at the Linwood mosque during Friday prayers.

Authorities have urged people in central Christchurch to stay indoors.

Police warned worshippers not to visit mosques "anywhere in New Zealand". A lockdown imposed throughout Christchurch was called off at about 05:00 GMT.

Police Commissioner Mike Bush said four suspects, including a woman, were in custody.

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

He said Australian security authorities were investigating any links between the country and the attack, but declined to provide further details about the Australian gunman.

"It is such a sad and devastating reminder of the evil that can be ever present about us," a visibily emotional Morrison said. (Aljazeera)

•Ambulance staff take a wounded man from outside the mosque in central Christchurch on Friday [Mark Baker/AP]

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