New Zealand Prime Minister Jacinda Ardern announces ban of all assault rifles after mosque shooting massacre

New Zealand's prime minister announced that assault rifles, such as the ones used last Friday in the massacre at two mosques in Christchurch, will be banned from the country once approved by the parliament.

"Today I am announcing that New Zealand will ban all military-style semi-automatic weapons. We will also ban all assault rifles. We will also ban all high capacity magazines," Prime Minister Jacinda Ardern said Thursday local time. "We will ban all parts with the ability to convert semi-automatic or any other type of firearm into a military style semi-automatic weapon."

Ardern said she expects the gun laws to be passed by the end of a "two-week sitting session" that concludes April 11.

Ardern said sellers should halt the sales of the banned weapons immediately and warned shops to return their stockpiles to suppliers. She said they didn't have an estimate for the number of assault rifles or military-style semi-automatic weapons currently in the country.

Residents caught with the banned guns will face the penalties, including fines of up to $4,000 and/or three years in prison, she said, noting that the new law could increase these penalties.

The country will also establish a buy-back scheme, which could cost between $100 million to $200 million, "a price that we must pay for the safety of our community," Ardern said.

The prime minister received praise for the announcement, including from Hillary Clinton. The former U.S. secretary of state seemed to take a shot at lawmakers back home, too.

"Under @jacindaardern's leadership, New Zealand has banned assault rifles and military-style semi-automatic weapons just six days after the Christchurch mosque attacks," the former U.S. secretary of state tweeted Thursday. "Public servants didn't stop at offering thoughts and prayers. They chose to act."

Ardern said Cabinet ministers made an in-principle decision to tighten gun ownership laws in a meeting immediately after the horrific shooting, which left 50 dead. The massacre marked the deadliest shooting in New Zealand history.

The Australian white supremacist charged in the attack had not been flagged by intelligence officials before the well-planned shooting.

Before the attack, New Zealand prided itself as one of the safest countries in the world -- a place where many police officers didn’t even wear their guns in public.

Chris Cahill, the president of the New Zealand Police Association, told ABC News that law enforcement officials might need to reconsider that officer gun policy now.

He said the country plans to conduct a thorough investigation into how they responded to the attack.

"We intend to learn some lessons from America as well," Cahill said in an interview Tuesday. "One is gun control can stop these and we will be having gun control in New Zealand and it’s a debate that America needs to have if the right people aren’t afraid.

"When I think about the reaction after shootings in the United States, it has been amazing to see how many people in New Zealand are rallying behind the Prime Minister’s push to strengthen the country's gun laws," Cahill added.

Ardern promised more changes could be coming with gun laws, including surrounding licensing, registration and storage.

ABC News' Darren Reynolds and Will Carr contributed to this report.