Thousands of hours of negotiations have been negated with the stroke of a pen.

LISTEN ABOVE: Senior fellow at US Council of Foreign Relations Edward Alden speaks to Rachel Smalley about the end of the TPP

Donald Trump has just taken the United States out of the TPP, saying it was "a great thing for the American worker, what we just did."

US president Donald Trump promised to kill the 12-country free trade agreement during the campaign for the Presidency.

It was among the first executive orders signed by the new President of the USA.

Speaking to Newstalk ZB yesterday, Prime minister Bill English said he still wants to see the deal happen, even if it doesn't give our exporters more access to the US market.

But Auckland University law professor Jane Kelsey said without that access, the TPP will do far more harm than good.

"It would give the US corporations all the things they wanted in the agreement for free, because the US wouldn't have to do anything in response."

Ms Kelsey said other crucial countries like Australia and Canada could also pull out.

"Both of those are having really significant political problems in getting approval through their legislative process."

Before the executive order was signed, CNN senior White House correspondent Jeff Zeleny said the decision will make quite an impact.

"If the US pulls out of course it is sort of like a stack of dominos, it may cause all of them to crumble."

The TPP was negotiated under Barack Obama but never ratified by Congress.

Mr Trump's executive order on the TPP is his administration's first major action on foreign policy.

It will send signals to Democrats and foreign leaders that he's putting his tough talk on trade into action.