It took New Zealand just six days to announce an immediate plan to change to the nation’s gun policy after a gunman killed 50 people at two mosques in Christchurch last week.

On Thursday, a day after the first victims were laid to rest, Prime Minister Jacinda Ardern announced a national ban on all military-style semiautomatic weapons, all high-capacity ammunition magazines and all parts that allow weapons to be modified into the kinds of guns used in last week’s attack.

Ms. Ardern is expected to encounter little resistance in Parliament. The new law could be in place as soon as April 11.

It is unclear how the weapons ban will be felt in New Zealand, where there are plenty of guns but relatively few murders. Since 2007, gun homicides have been in the single digits every year except in 2009, when there were 11.