Police have taken four suspects - three men and one woman - into custody.
Police Commissioner Mike Bush said earlier: "There is no guarantee the risk is limited to Canterbury and we need all New Zealanders to be extra vigilant".
Mass shootings, and violent crime in general, are rare in New Zealand, a country of almost 5 million people. He appeared to have begun buying guns the following month, she said.
Those new amendments included greater oversight over the acquisition of ammunition, restricting sales to only firearms license holders and requiring permits for people to order guns or ammunition by mail, updating and adding more information including photographs to individuals'gun licenses, and requiring secure storage for guns.
People pay their respects at the memorial service held at the Port Arthur historic site for the 35 victims of the Port Arthur massacre, May 19, 1996.
"Police are responding with its full capability to manage the situation, but the risk environment remains extremely high", he said in a release on Friday.
Brenton Tarrant, a 28-year-old Australian man, identified himself online as being behind the attack.
By comparison, there have been 2,740 gun deaths in the United States in the first two and a half months of this year, according to the Gun Violence Archive. Health officials said 48 other people were being treated at Christchurch Hospital for gunshot wounds.
That number has grown consistently throughout the years, with New Zealand reporting only 1.3 million such firms in 2016, 1.2 million in 2009 and less than a million in 2005.