"The key is that a small group of organised provocateurs can [overwhelm] a lightly armed police force trying to defend a relatively large piece of real estate. This is very serious."
Buchanan said avoiding complacency and using intelligence more competently could help.
"The good thing is, the intelligence was there that there'd be an assault on the Capitol. But it was ignored by the political appointees in the Trump administration."
In the US, the Presidential administration appoints more than 4000 people, including staff in the defence, homeland security and justice agencies.
Buchanan said New Zealand's public service and security agencies were less politicised, so the risk of collusion with any seditious protest group was probably smaller than in the US.
Trump supporters attempted to disrupt Congress and forestall the certification of Joe Biden as President. Photo / AP
But he added: "We know that there are elements in the police and the armed forces that hold extremist views.
"Lest we think we're in a benign security environment, we're not."
Buchanan, director of 36th Parallel Assessments, said assorted militant groups openly organised the Capitol assault online.
He said attackers used a big crowd of Donald Trump supporters as cover before assaulting US Capitol Police with sophisticated tactics.
Trump supporters try to break through a police barrier at the Capitol building. Photo / AP
"They were assaulting the officers with improvised weapons. They'd then rotate out."
"They would do that until the Capitol officers had to retreat because they were physically tired."
Police were called to the Parliamentary precinct in Wellington on Wednesday morning after an axe-wielding man allegedly smashed glass doors. Photo / Supplied
National security expert and Army veteran Dr Jim Rolfe said New Zealand's political culture was less polarised than America's.
He said domestic divisions over the Vietnam war in the 1960s and the Springbok tour of 1981 had no current parallels.
"This becomes a major issue if there are those cultural identity splits," said Rolfe, a former security adviser to the Department of Prime Minister and Cabinet.
He did not believe a copycat attack on the Beehive was a major risk but expected officials in security agencies to be studying the issue closely.
"Quite frankly, the officials are up on this far more than the ministers are."
"It very likely is that the current level of security is sufficient," Rolfe said.
Sen. Mitch McConnell makes emotional speech slamming effort to overturn Electoral College votes: "We cannot keep drifting apart into two separate tribes with a separate set of facts and separate realities with nothing in common except our hostility for each other." pic.twitter.com/nrmPct1R4G
Police on Wednesday morning arrested a 31-year-old man allegedly seen with an axe outside Parliament.
It was not immediately clear why he attacked the glass doors.
A cordon with yellow tape was seen near smashed glass, as were barriers to stop cars driving up to the building.
In a statement issued on Wednesday afternoon, Parliamentary Service Chief Executive Rafael Gonzalez-Montero said security breaches at Parliament were rare.
A full review of the incident would start, and the service would assess if changes to security measures were needed.
"This morning's incident was unfortunate, but managed well by Parliamentary Service Security."
