New Jersey Governor Chris Christie's aide Bridget Anne Kelly fired over gridlock on George Washington Bridge

IT WAS supposed to be an act of revenge. But this simple email shut down the world's busiest bridge and left a woman dead. Now the "humiliated" man in charge is paying the price.

IT WAS politics at its most petty and vindictive.

Staff of US rising star and New Jersey Governor Chris Christie deliberately caused a traffic jam on one of the country's busiest bridges to punish a political rival, according to emails and text messages released amid an investigation on Wednesday.

The traffic gridlock delayed emergency responders from attending four medical situations - including one where a 91-year-old woman died - thanks to the unannounced closures of access lanes.

Commuters and schoolchildren were trapped in back-ups for hours on the George Washington Bridge.

"Time for some traffic problems in Fort Lee,'' Mr Christie's deputy chief of staff, Ms Kelly, wrote in August in a message to David Wildstein, a top Christie appointee on the Port Authority of New York and New Jersey.

"Got it,'' Mr Wildstein replied. A few weeks later, Mr Wildstein closed two of three lanes connecting Fort Lee to the bridge.

Before the correspondence was released there had been speculation whether the huge traffic back-up was retribution against the mayor of Fort Lee for not endorsing Mr Christie for re-election last autumn.

Mr Christie, a leading hopeful for the Republican Party's presidential nomination in 2016, said he was "embarrassed and humiliated'' by the emails and text messages.

After the messages were reported on Wednesday, he cancelled public appearances and several hours later issued a statement saying he was "outraged and deeply saddened'' by the revelations.

He said he was misled and he denied involvement. He told reporters overnight that he has fired Ms Kelly because she lied to him.

"We fell short of expectations,'' Mr Christie said, adding that he was "stunned by the abject stupidity'' shown in the incident. He said he is responsible for what happened and said he would to go to the affected town to apologise.

"I had no knowledge or involvement in this issue, in its planning or execution,'' he added.

The revelations raise new questions about his leadership on the eve of his second term designed to jumpstart his road to the White House.

Democrats at the national level swiftly circulated the news of the scandal, calling it more evidence that the potential Republican candidate for president in 2016 is a bully.

Some conservative Republicans who have been stung by Mr Christie's comments in the past joined in.

Even if Mr Christie navigates this challenge quickly, it will almost surely come back to haunt him in a presidential run, said Republican operative Hogan Gidley.

"I don't necessarily think it's Christie's policy that's going to ultimately catapult or sink his campaign; I think it's his personality,'' Mr Gidley said.

The messages do not directly implicate Mr Christie in the shutdown.

Fort Lee Mayor Mark Sokolich, a Democrat, called it "appalling'' that the traffic jams appear to have been engineered.

Mr Sokolich said the gridlock put people in danger by holding up emergency vehicles, and he added that those responsible should resign.