He also questioned why some media outlets were not referring to it as a terrorist attack.
Witness describes the shooting as it happened in a Christchurch mosque
"I can sense that media is not portraying [this] as a terrorist attack. It is a terrorist attack. It is organised. For me this is a terrorist attack. This proves that terrorism has no faith affiliation or ethnicity."
He offered condolences to the victims and urged the Muslim community to "follow the law and restrain themselves. We must not react in New Zealand and Australia".
Greens Senator Mehreen Faruqi, Australia's first female Muslim senator, went even further than the grand mufti.
"There is blood on the hands of politicians who incite hate. To me, there is a clear link between their politics of hate and this sickening, senseless violence in Christchurch," she tweeted.
"Muslims have been targeted during Friday prayers. This is not an isolated event with mysterious causes. This is not random. This is the consequence of the Islamophobic and racist hate that has been normalised and legitimised by some politicians and media," she added.
"We know Muslims are directly targeted by politicians day after day including those on the far-right like Pauline Hanson and Fraser Anning. We know Muslims are demonised constantly. We know we are hated by some."
While Muslims Australia - Australian Federation of Islamic Councils also said the attack was "a product of the ever-increasing Islamophobia and marginalisation of Muslims".
"[It is] a reminder to all concerned, including political leaders and media commentators, of the horrific consequences that an atmosphere of hate and division can lead to. No country or community is immune to such atrocities," it said in a statement.
"We urge governments in Australia, both at a Federal and State level, to give extra attention to the rise of anti-Muslim sentiment and extremism."
Late Friday, Prime Minister Scott Morrison confirmed an Australian is now in custody over the attacks.
"Australian authorities are involved and they will be proceeding with their investigation," he said.
New Zealand Police Commissioner Mike Bush confirmed on Friday afternoon that police had arrested four people, three men and one woman, but said he wouldn't "assume that the threat is over".
He added that he was not aware of other people being involved, but said: "we cannot assume there are not others at large".
Mr Bush also confirmed that reports of improvised explosive devices being strapped to vehicles had been deemed safe by defence force personnel.
New Zealand Prime Minister Jacinda Ardern said it was "one of New Zealand's darkest days", describing the incidents as "an unprecedented act of violence".
Additional reporting: Maani Truu, AAP