Image copyright Anwar Hussein / Getty Images Image caption At the time, police reportedly said the gunshot noise was a sign falling over

A teenager tried to kill Queen Elizabeth II during a visit to New Zealand in 1981, declassified official documents confirm.

Christopher Lewis, 17, fired a shot as the Queen toured the city of Dunedin, New Zealand's Security Intelligence Service (SIS) said.

Police had said at the time that the gunshot sound had been caused by a sign falling over, local media report.

A former police officer and local media have suggested a cover-up took place.

New Zealand feared future royal tours could be cancelled, it is claimed.

The royal parade took place in Dunedin on 14 October 1981. Police and members of the public heard "what they took to be a shot", according to the declassified documents obtained by news website Stuff.

Lewis was arrested shortly afterwards and police discovered a rifle and used gun cartridge in a building overlooking the parade.

"Lewis did indeed originally intend to assassinate the Queen," the documents say. But he "did not have a suitable vantage point from which to fire, nor a sufficiently high-powered rifle for the range".

Lewis was not charged with attempting to kill the Queen but was accused instead of offences including discharging a firearm.

An SIS memo written shortly after Lewis's first court appearance and obtained by Stuff said officials feared journalists would connect Lewis to the Queen's parade.

"Current police investigations into the shots have been conducted discreetly and most media representatives probably have the impression that the noise was caused by a firework of some description," the memo said.

"There is a worry, however, that in court the press may make the connections between the date of the offence and the Queen's visit."

The New Zealand government was accused of covering the incident up by former Dunedin police officer Tom Lewis in 1997.

He told Stuff he doubted the full truth would emerge.

"It will be like ripping the scab off... so much pus would come out," he said.

The New Zealand authorities feared that if the incident became public knowledge, future royal visits could be called off, Stuff said. Tom Lewis said the teenager was initially facing a charge of attempted treason but that subsequently changed.

Colin Peacock of Radio New Zealand said journalists had come forward in recent weeks to say they were visited by police and told not to report "anything about a shot or any sharp sound that was fired". "They do believe this came from the very very top and shut down the story," he told the BBC.

Lewis told investigators he was the commander of an armed group but the SIS investigated the claim, found no evidence and said Lewis suffered "delusions".

After serving his initial jail term he went on to commit armed robberies and was charged with murder. He took his own life in prison in 1997.

New Zealand police have said they will investigate Lewis's case file given the interest in the "historic matter", the New Zealand Herald reported.