New Zealand's Parliament was briefly thrown into chaos when a man tried to jump from the public gallery into the debating chamber.

The man muttered something about injustice before attempting to climb over a low barrier during a routine parliamentary session.

He was just able to be restrained by a security guard and four or five people who were watching the debate.

Had he succeeded in getting over the barrier, the man would have fallen about 12 feet on to desks and politicians below.

Prime Minister John Key initially blamed his political opponents in the Labour Party for the incident. The two parties have been squabbling over the level of security detail needed for Mr Key.