New Zealand Police Commissioner Mike Bush says he believes police officers stopped the gunman who killed 50 people at two mosques on his way to another attack.

Zaed Mustafa, in wheelchair, brother of Hamza and son of Khalid Mustafa killed in the Friday, March 15 mosque shootings reacts during their burial at the Memorial Park Cemetery in Christchurch, New Zealand, Wednesday, March 20, 2019 [Photo:AP]

Bush says they believe they know where the gunman was going but won't say more because it's an active investigation.

In a 74-page manifesto he released before the attack, accused Australian gunman Brenton Tarrant said he was going to attack mosques in Christchurch and Linwood, and then one in the town of Ashburton if he made it that far.

Bush also revised his timeline, saying officers rammed the suspect off the road and arrested him 21 minutes after the first emergency call rather than 36 minutes.

Bush says FBI agents have traveled to New Zealand to help with the investigation.