People across New Zealand are observing the Muslim call to prayer as the nation reflects on the moment one week ago when 50 people were slaughtered at two mosques.

Prime Minister Jacinda Ardern and thousands of others congregated in leafy Hagley Park opposite the Al Noor mosque in Christchurch to observe the call to prayer early Friday afternoon.

Thousands more were listening in on the radio or watching on television as the event was broadcast live. The prayer was followed by two minutes of silence.

The observance comes the day after the government announced a ban on "military-style" semi-automatic firearms and high-capacity magazines like the weapons that were used in last Friday's attacks.