Dec 4 (Reuters) - The operator of New Zealand's stock exchange said on Friday that two independent reviews into system issues this year, including August's cyber attack, have been completed and the undisclosed recommendations were being implemented.

It has been an unprecedented year for the bourse operator, NZX Ltd, whose systems were overwhelmed in March and April by trading volumes that were as high as six times their daily averages in 2019 due to the coronavirus pandemic, and by a week of cyber attacks in August.

The separate reports confirmed that the two incidents were not connected.

InPhySec, an independent cybersecurity firm tasked with reviewing the cyber attacks, said "the volume, sophistication and persistence of the attacks were unprecedented in a New Zealand context, and are amongst the most severe we are aware of to have been experienced internationally."

The InPhySec review recommended several technical and process steps to strengthen security and closer communications with the broader cybersecurity community, according to NZX.

The key findings were being shared privately with financial market regulators and senior market participants, said NZX Chief Executive Mark Peterson.

He noted that InPhySec had highlighted the risks of exacerbating attacks through media coverage, and said NZX would continue to follow official advice not to disclose details of an attack or its response.

The Ernst & Young report into trading system issues highlighted the need for changes to older systems. NZX has since set up a new technology committee. (Reporting by Arpit Nayak in Bengaluru, additional reporting by Nikhil Kurian Nainan Editing by Marguerita Choy)