Melbourne: Australian counter-terrorism police on Monday searched two homes linked to the family members of the gunman accused of killing 50 people at two mosques in Christchurch to obtain material that may assist New Zealand Police in their investigation into the terror attack.

The attacker, identified by authorities as Australia-born Brenton Tarrant, 28, targeted immigrants during Friday prayers. Witnesses said victims were shot at close range.

He was arrested shortly after entering two mosques --Masjid Al Noor and Linwood - with high-powered weapons and shooting dead 50 people, including five Indians.

The New South Wales (NSW) Joint Counter Terrorism Team on Monday two properties on the state's mid-north coast.

One of the properties being searched belongs to Sharon Tarrant, the mother of the attacker.

''Around 8.30 this morning (local time) officers from the NSW JCTT executed a search warrant at a home in the town of Sandy Beach, near Coffs Harbour. A short time later, a second search warrant was executed at another home in Lawrence near Maclean,'' the statement said.

''The primary aim of the activity is to formally obtain material that may assist New Zealand Police in their ongoing investigation,' it said adding ''the family of the Australian man arrested in Christchurch continues to assist police with their inquiries.'

Police further assured the community that that there was no information to suggest a current or impending threat related to this search warrants.

The NSW JCTT comprises representatives from the Australian Federal Police, NSW Police Force, the Australian Security Intelligence Organisation (ASIO) and the NSW Crime Commission.

In an interview with Nine News, Tarrant's family expressed shock and apologised for his role in the shooting.

His uncle, Terry Fitzgerald, mourned the victims in Christchurch.

"We are so sorry for the families over there, for the dead and injured," he said.

His grandmother, Marie Fitzgerald, told reporters she could not fathom how "somebody in our family would do anything like this.

The 81-year-old said her grandson was "obviously not of sound mind.

The family had dinner with Tarrant 12 months ago for his sister's birthday in Grafton.

Tarrant, a self-avowed white supremacist, lived in Grafton, 500km northwest of Sydney, where he worked as a personal trainer at Big River Gym. He moved to the New Zealand city of Dunedin at some point in the last two or three years.

Tarrant did not request bail during a brief court appearance on Saturday and will next appear on April 5. He has been charged with one count of murder but further charges are expected.

Australian Home Affairs Minister Peter Dutton defended the ASIO and the Australian Federal Police against suggestions they had failed to identify the danger Tarrant posed.

He said Monday that Tarrant had spent only 45 days in Australia over the past three years and was not on any terror watch lists.

His social media ravings were missed because of the massive amount of digital traffic which has to be monitored.

"There is only so much content that can be covered, assessed and analysed by ASIO and other partner agencies," said Dutton.

He also rejected claims the security authorities were only focused on Islamic terrorists, ignoring right-wing extremists.

Dutton said Australia's security agencies are very concerned about retaliatory or copycat attacks in the wake of the Christchurch terror attack.

Tarrant's travels through Europe, Turkey and Asia are now being examined in detail, in part to see if he had any overseas help in carrying out the massacre.