Cambodia, home of the Angkor Wat temple, is among the 16 countries involved in the trade talks.

A massive free trade deal under negotiation in Auckland this week could "dwarf" the controversial Trans-Pacific Partnership Agreement, Trade Minister Todd McClay says.

On Monday morning Trade Minister Todd McClay opened negotiations for the Regional Comprehensive Economic Partnership (RCEP) trade deal at Sky City.

Sixteen countries are involved in the RCEP including the 10 members of ASEAN - Brunei-Darussalam, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam.

JOHN HAWKINS/FAIRFAX NZ Trade Minister Todd McClay says the Regional Comprehensive Economic Partnership will benefit New Zealand businesses and the wider economy.

The other countries have free trade agreements with the ASEAN group - Australia, China, India, Japan, Korea, and New Zealand, collectively known as the ASEAN Free Trade Partners.

READ MORE: TPPA signing: Thousands take to the streets as trade deal is made official

McClay said a RCEP free trade agreement would benefit the economy and give New Zealand businesses better access to the region.

Benefits included better market access for businesses throughout the region, elimination of tariffs for exporters, more consistent rules for horticulture trade, improved customs procedures and rules of origin, more opportunities for New Zealand's service sector and improved protection for investors to encourage more investment between the countries.

The model for New Zealand's public drug agency Pharmac was not up for negotiation, nor was the ability to pass New Zealand's laws and regulations fairly and transparently, McLay said.

Formal negotiations started in May 2013 with 12 rounds held so far, the most recent in Perth in April.

The deal could be signed before the end of the year at the earliest, McClay said.

The agreement is intended to deepen economic integration between countries so businesses can operate more effectively and efficiently throughout the region, improving on the region's "noodle bowl" of rules.

New Zealand already has free trade agreements with some of the countries involved in RCEP, and has concluded Trans-Pacific Partnership Agreement (TPPA) negotiations with several others.

Existing free trade agreements will remain in place, and RCEP will help create new free trade relationships where they do not already exist. It may also be an opportunity to improve some existing agreements.

McClay said it was one of the most important trade deals New Zealand had been involved in.

If successful it would provide a single set of trade rules for almost half of the world's population.

It will cover a region with more than 3 billion people, accounting for almost a third of world trade, totalling US$23 trillion (NZ$33 trillion) in GDP.

The economic gains of RCEP would even dwarf those of the TPPA, McClay said.

"It could be the means to bring some of the biggest and most important economies in the world together."

Many people in the region believed trade was good for countries, but were not sure if trade was good for them, he said.

But, an increase in trade boosted national GDP which improved standards of living.

"Trade openness is good for our economies, it is good for our citizens," McClay said.

The Auckland negotiations will run until Saturday.

In contrast to the TPPA, the public was invited to join discussions about the deal either in person or online.

A public session providing an overview of the RCEP negotiations followed by a question and answer session would be held on Tuesday from 5.30pm at the Sky City Convention Centre.

A live stream would be available during which questions could be submitted online.

When the TPPA was signed in Auckland in February, thousands of protesters marched the streets opposing the deal, fearing it was not in the best interest of New Zealanders.

There was also criticism that the Government had not communicated the TPPA effectively.

McLay said he hoped that would not happen with this deal.

"Leave your protests and your placards outside and come and join the conversation."

There would also be a public session with negotiators on Tuesday at 3pm.