The US-led Trans-Pacific Partnership, one of the biggest trade deals in history, was signed in New Zealand on Thursday as protestors demonstrated over fears for jobs and sovereignty.

   The ambitious deal, promising the elimination of nearly all tariffs among the 12 member nations, aims to break down trade and investment barriers between countries accounting for about 40 percent of the global economy.

   While New Zealand Prime Minister John Key and US Trade Representative Mike Froman lauded the pact at the ceremonial signing in Auckland, thousands of protestors blocked roads outside.

   "Today is a significant day, not only for New Zealand but for the other 11 countries in the Trans-Pacific Partnership," Key said.

   US President Barack Obama hailed the signing, saying the TPP would give the United States an advantage over other leading economies, namely China.

   "TPP allows America -- and not countries like China -- to write the rules of the road in the 21st century, which is especially important in a region as dynamic as the Asia-Pacific," Obama said in a statement from Washington.

   He called the TPP "a new type of trade deal that puts American workers first."

   "Put simply, TPP will bolster our leadership abroad and support good jobs here at home," he added.

   However, protesters argue it will cost jobs and impact on sovereignty in Asia-Pacific states.

   Australia's Trade Minister Andrew Robb said the TPP would see the elimination of 98 percent of tariffs among the 12 states.

   Although the signing marks the end of the negotiating process,  members still have two years to get the deal approved at home before it becomes legally binding.

   "We will encourage all countries to complete their domestic ratification processes as quickly as possible," Key said.

   "TPP will provide much better access for goods and services to more than 800 million people across the TPP countries, which make up 36 percent of global

GDP."

   The agreement was signed by Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.

   "Other countries have already signaled an interest in joining TPP," Key said. "And this could lead to even greater regional economic integration."

   In a joint statement ministers representing the 12 countries said the TPP "will set a new standard for trade and investment in one of the world fastest growing and most dynamic regions.

   "Our goal is to enhance shared prosperity, create jobs and promote sustainable economic development for all of our nations."

   Froman had earlier warned against any delay in endorsing the deal.

   "After five years of negotiation, signing the TPP is an important milestone in our efforts to set high-standard rules of the road in the Asia-Pacific region and more generally, and to deliver an agreement that will benefit American workers, farmers and businesses," he said.

   Claiming the deal stands to add $100 billion a year to US economic growth, Froman added: "There are costs to delay, real economic costs."

   Groups opposed to the TPP have expressed concern about the secrecy in which the negotiations were conducted, the potential erosion of a country's sovereignty and say it is weighted in the United States' favor.

   About 2,000 people took part in several protests in central Auckland, many blocking key road intersections.

   A leading TPP opponent in New Zealand, law professor Jane Kelsey, wrote in the New Zealand Herald that the agreement guaranteed foreign states and corporations "a right of input into regulatory decisions" which local organizations would not have.

   "More than 1,600 US companies, the most litigious in the world, will gain new rights they can enforce through private offshore tribunals if/when regulation damages their value or profits," she said.

   Amid speculation that members of the US Congress will not want to risk alienating voters by approving it ahead of the November presidential election, Obama on Tuesday discussed ratification with Republican leaders who said they still had problems with the complex deal.

   New Zealand is acting as the TPP depositary, taking responsibility for administrative functions. (AFP)