New Zealand is enduring "one of the darkest days" in its history after the terrorist attacks on two mosques in Christchurch on Friday afternoon left 49 people dead and 48 others injured.

The unprecedented terrorist attacks took place at around 3 p.m. local time (0300 GMT), when a gunman reportedly walked into a mosque with semi-automatic weapon and opened fire.

Police later confirmed that two mosques in central Christchurch had been attacked and multiple deaths were feared. Witnesses said there was much blood and multiple deaths. At least 50 rounds of gunshots were heard during the shooting, said one witness.

The Armed Squad was placed at the scene with additional Defense Force deployment. Four suspects were soon arrested with three of them born in Australia. One of the suspects is a woman.

Police commissioner Mike Bush confirmed later that 49 people were killed and 48 others injured in the shooting.

It is understood to be a well-planned terrorist attack, with further bombs discovered in cars located in Christchurch central by the police. One of the gunmen live-streamed the shooting via social media. His manifesto was also circulated online.

However, the killers were not on any watch list confirmed by the authorities.

After the attacks, New Zealand Prime Minster Jacinda Arden addressed the public, describing Friday as "one of the darkest day in New Zealand."

She also strongly condemned the terrorist attack, saying "You might have chosen us; we utterly reject and condemn you."

Ardern said New Zealand was not a target because it is a safe harbour of those who hate, nor because New Zealand condones racism or is an enclave for racism.

She said New Zealand represents kindness, compassion and a home for those who share New Zealand's values.

"Those values, I can assure you will not and cannot be shaken by this attack."

After the attacks, the New Zealand government adjusted the national safety level from low to high, the first time that the country's threat level has been raised to this level.

People have been recommended by the police to stay inside. All mosques across the country have been urged to shut their doors, and people have been advised to refrain from visiting these premises until further notice.

Christchurch streets and schools were locked down after the gun shooting. School lock-down was lifted until 6 p.m. local time.

Blood supply in Christchurch is under pressure. A local community organization has urged the public to donate blood.

People across New Zealand are expressing their condolences to the victims. Flowers, candles and notes have been placed near the mosques where the shooting took place.

Christchurch airport is operating as normal. However, outbound flights have been cancelled, in addition to multiple delays.