GREENSBORO, North Carolina (AFP) - Mr Donald Trump branded a US pastor a "nervous mess" on Thursday (Sept 15), a day after she shut him down as he criticised White House rival Hillary Clinton, prompting a sharp rebuke from the Democratic nominee.

Mr Trump had travelled to the suffering Michigan city of Flint in part to learn about how it has dealt with a major public health crisis prompted by the lead contamination of its drinking water.

But when the Republican presidential hopeful arrived at Bethel United Methodist Church, a predominantly black congregation, he turned political, assailing Mrs Clinton for having "failed on the economy, just like she's failed on foreign policy."

"Everything she touched didn't work out. Nothing," he said.

As he spoke, Reverend Faith Green Timmons walked over, her hands clasped, and interrupted him.

"Mr Trump, I invited you here to thank us for what we've done in Flint, not to give a political speech," Reverend Timmons said in a low voice.

"Oh, oh, oh, OK," Mr Trump said, appearing somewhat flustered before shifting his remarks to conditions in Flint.

On Thursday, Mr Trump told Fox News that he felt "something was up" when Reverend Timmons introduced him.

"Everyone plays their games, it doesn't bother me," he said, suggesting that the pastor might have had a political motive for stepping in.

"She was so nervous, she was like a nervous mess," he said.

Mrs Clinton herself had been sidelined by a bout of pneumonia for three days this week. But on Thursday she returned to the campaign trail in North Carolina, where she weighed in on the Flint affair.

"He called her a nervous mess," Mrs Clinton noted to reporters after a campaign rally in Greensboro. "That's not only insulting, it's dead wrong."

Reverend Timmons "is a rock for her community in trying times," Mrs Clinton said. "She deserves better" than Mr Trump's criticism.

Mr Trump insisted on Fox that those at the church had been welcoming.

"What really made me feel good, the audience was saying, 'Let him speak, let him speak.' The audience was so great," he said.

He clearly has been more disciplined on the campaign trail in recent weeks, following a year of pointed rhetoric that has antagonised many.

But his criticism of the pastor - 11 days after he visited a black church in nearby Detroit and courted African-American voters - highlights his willingness to stray from that regimen in order to push back against perceived affronts.