The Royal Commission into the Christchurch terror attack begins work today.

The Commission has been established to answer questions New Zealanders and the government have about why and how the 15 March terror attack was able to happen. It will gather information about how to prevent any similar attacks.

Jacqui Caine, the former ambassador to Chile, was announced as second commissioner joining Supreme Court Justice Sir William Young, who was previously announced as the chairperson.

The pair would begin by establishing how they would carry out the investigation, a spokesperson for the prime minister said, and will report back to the Governor General with their findings on 10 December.

"It's a relatively tight timeframe for a royal commission, so we're keen for them to get under way," the spokesperson said.

"They have the powers to call people to appear before them ... they have the ability to look through a lot of material, and their powers are very broad.

"We want them to leave no stone unturned."

Agencies directed to cooperate include the police, Ministry of Justice, the New Zealand Security Intelligence Service, Government Communication Security Bureau, and Immigration New Zealand.

All have agreed to cooperate with the investigation.

The commission will look at what actions agencies took, whether they could have done anything to prevent the attack, and what barriers there were.

It will investigate the gunman's activities before the attack in New Zealand and abroad. It will look at how he got a gun, a licence and ammunition, his use of social media, and his connections to others.

The commission has also been asked to engage with New Zealand's Muslim community.

New Zealanders have the right to ask questions about the attack.

The Royal Commission has a budget of $8.2 million.