New Zealand tourism industry and government officials are stepping up efforts to assure visitors that the country's adventure activities are safe following a damning inquest into the deaths of nine people during a skydiving aircraft crash in 2010.

Labor Minister Simon Bridges announced on Wednesday that the government had approved three companies to audit adventure activity operators according to new safety regulations issued in 2011.

The announcement follows the release in March of a new safety audit standard that operators must pass before being eligible for registration.

"New Zealand is renowned for its adventure tourism and the safety audit standard is one of a number of initiatives introduced over the last three years to strengthen the safety of the industry, " Bridges said in a statement.

The three providers would soon begin targeted auditing of the country's estimated 1,500 adventure activity operators, and from Nov. 1 next year, it would be an offence to provide an adventure activity without being audited, he said.

The announcement followed a claim from the Tourism Industry Association New Zealand (TIA) Tuesday that significant advances had been made to improve safety in the burgeoning adventure tourism sector since the aircraft crashed.

"Awareness of safety in the sector has never been higher. It's critical that 'adventure' remains in adventure tourism, but we all have a responsibility to ensure that these experiences are being delivered within a strong safety framework," TIA Chief Executive Martin Snedden said in a statement.

Changes included the introduction of a world-first Adventure Aviation Rule that included a range of requirements for operators and the Civil Aviation Authority (CAA) had introduced strict requirements for pilots and operators to focus on pre-flight weight and balance calculations.

"The safety work we are doing in New Zealand is being noted internationally and I'm confident it will keep our adventure sector on the leading edge."

A coroner on Monday released his report into the deaths of the four overseas tourists, four skydiving instructors and the pilot in the crash of a Walter Fletcher FU24 aircraft at Fox Glacier, in the South Island.

The report criticized the fact that seating restraints were not used, which probably caused a load shift in the critical take-off and climb phase of the aircraft.

The families of the four tourists killed in the crash -- from Ireland, Australia, Germany and England -- on Monday issued an open letter to Prime Minister and Tourism Minister John Key, describing the inquest report as "disturbing" and saying it showed the need for "compelling and urgent" action to improve safety standards.

"We believe it is essential that your government takes very decisive and unequivocal action to reassure the world that New Zealand is a very safe place to visit," said the letter.