She warned Zimbabwe's humanitarian crisis would worsen. Meanwhile, it is reported that power-sharing talks have stalled because of insults traded between the opposition and mediator Thabo Mbeki. Representatives of the opposition Movement for Democratic Change and President Robert Mugabe's Zanu-PF had resumed talks in South Africa earlier in the week.
At a news conference in New York, Ms Bragg called for "massive" international assistance for Zimbabwe. In addition to the cholera outbreak, which has killed more than 360 people since August, she said there has also been a breakdown in both the health and education sectors.
“For a country that used to have over 90% school attendance, now we're seeing less than 20%,” she said.
As well as teachers not being able to afford to work, students were required to make payments in kind, including food, which they did not have, she said.
Zimbabwe used to have one of the best education systems in Africa.
Earlier, MDC leader Morgan Tsvangirai said the cholera outbreak was "the greatest threat ever to face" the country.
Mr Tsvangirai is in South Africa to attend the talks, which are reported to be making little progress.
A letter from South Africa's former leader Mr Mbeki, who negotiated September's deal between the MDC and Zanu-PF, has been leaked to the press.
In a 10-page response dated 22 November to the MDC questioning his impartiality, he accused the opposition of not respecting Africa leaders and paying too much heed to the West, South Africa's Business Day newspaper reports.
"It may be that, for whatever reason, you consider our region and continent as being of little consequence to the future of Zimbabwe, believing that others further away, in western Europe and North America, are of greater importance," Mr Mbeki wrote in the letter also quoted on the ZimOnline news agency website.
He said the MDC had denounced regional leaders as "cowards".
"Such manner of proceeding might earn you prominent media headlines. However, I assure you that it will do nothing to solve the problems of Zimbabwe," Mr Mbeki said.
On Wednesday, Mr Tsvangirai repeated calls for Mr Mbeki to go as mediator.
"He does not appear to understand how desperate the problem in Zimbabwe is, and the solutions he proposes are too small," Mr Tsvangirai said in a statement, AFP news agency reports.
"He is not serving to bring the parties together because he does not understand what needs to be done."