Two explosives were also found rigged to a single vehicle.
Malaysian Prime Minister Mahathir Mohamad said he hoped New Zealand "will arrest these terrorists and do the necessary under the law of the country".
Prime Minister Jacinda Ardern gives a press conference from Wellington. Credit PA
He adds that one person has been taken into custody, but warns it is unclear if more than one person is involved, or if any other locations are under threat.
British Queen Elizabeth II also sent a message to the people of New Zealand on Twitter, and said "I have been deeply saddened by the appalling events in Christchurch today". "Police are responding with its full capability to manage the situation, but the risk environment remains extremely high".
At least 48 people, some in critical condition, were being treated at Christchurch Hospital for gunshot wounds, authorities said. "I am calling on the world, in particular the West, to take quick measures", he said.
A spokesman for New Zealand's interior ministry said the video is likely to be classified as objectionable content under local law, and could be illegal to share. For many, this may not have been the place they were born, in fact for many, New Zealand was their choice. "It must have been an automatic - no one could pull a trigger that quick", the man, who did not wish to be named, told AFP.More news: Trump issues first veto after rebuke of border order
Seven people were killed during this attack.
The 74-page dossier by Brenton Tarrant, which has been described by Australian Prime Minister Scott Morrison as a "work of hate", praised Trump as "a symbol of renewed white identity and common purpose". "They have no place in New Zealand".
He said that at least 49 people were confirmed dead.More news: Ethiopian Airlines says analysis of flight recorders has begun
"On behalf of my country, I offer my condolences to the Islamic world and the people of New Zealand, who have been targeted by this deplorable act - the latest example of rising racism and Islamophobia", he added. "Clearly what has happened here is an extraordinary and unprecedented act of violence".
Police urge all mosques across New Zealand to shut their doors and advise people to refrain from visiting them until further notice.
Indonesia's ambassador to New Zealand, Tantowi Yahya, told Reuters inquiries were being made as to whether Indonesians were caught up in the attack.
New Zealand media reported that between nine and 27 people were killed, but the death toll could not be confirmed.More news: Android Q Beta 1 Rolling out to Pixels Devices - Details
Asked if the police were searching for any other suspects, he said: "We never assume that there aren't other people involved, that's why we've got an vast presence out there ... but we don't have named or identified people that we are looking for, but it would be wrong to assume that there is no-one else".