The top prosecutor in the Georgia election case against Donald Trump took the stand to vigorously defend her relationship with a fellow prosecutor during a combative hearing on Thursday.

Mr Trump's lawyers alleged that Fulton County District Attorney Fani Willis's relationship with Nathan Wade, whom she hired, proved a conflict of interest.

The claims could upend the election-subversion charges against Mr Trump.

Over two hours of heated testimony, Ms Willis looked increasingly aggravated.

"It is a lie, it is a lie," she said at one point in response to questions, prompting a visibly perplexed Judge Scott McAfee to call a brief recess.

The first female district attorney in Fulton County, Ms Willis charged Mr Trump and 18 co-defendants last year with conspiring to overturn the former president's 2020 election loss to Joe Biden in Georgia.

But last month, that case was undermined by claims from one of Mr Trump's co-defendants, Mike Roman, who said Ms Willis and Mr Wade - who she hired as special prosecutor for the Trump case in late 2021 - had an improper relationship and benefitted financially from the arrangement.

In a legal filing, Mr Roman alleged Ms Willis overpaid Mr Wade for the special counsel role and that the two took luxury holidays together that were paid for by Mr Wade. Those trips included two cruises to the Bahamas, and trips to Napa Valley, California, and Caribbean resorts in Aruba and Belize.

Both Ms Willis and Mr Wade acknowledged the relationship in early February, but they have denied any conflict of interest or financial impropriety.

On Thursday, defence lawyers pushed both Ms Willis and Mr Wade on how he was reimbursed for his work and whether Ms Willis repaid him for her share of vacations while they were dating.

Ms Willis is an "independent strong woman... she is going to pay her own way", Mr Wade testified, adding she typically paid him back in cash, meaning no records were available.

The district attorney offered a more forceful counter, saying she didn't "need anybody to foot my bills".

At other points in her testimony, Ms Willis worked to bring the attention back to Mr Trump's case.

"You're confused. You think I'm on trial. These people are on trial for trying to steal an election in 2020," she said to lawyer Ashleigh Merchent, referring to the main case.

Ms Willis' testimony followed that of a former friend and employee, Robin Yeartie, who claimed the district attorney's relationship with Mr Wade began before he joined the Trump case - contradicting both of their timelines.

She saw the pair hugging and kissing years before the case, Ms Yeartie told the court, so she had "no doubt" the relationship started in 2019.

Ms Willis offered a fiery counter to her former friend, insisting no romantic relationship began until two years later. And she echoed claims made by Mr Wade in court. He claimed that his cancer diagnosis in 2020 would have prevented a physical relationship.

"Mr Wade had a form of cancer that makes your allegations somewhat ridiculous," she told defence lawyer Steven Sadow. "I'm not going to emasculate a black man … so I don't think we should discuss it further."

Judge McAfee has said he could disqualify Ms Willis from the case if evidence supports the defence's claims. Ms Willis' removal would delay and potentially derail the proceedings against Mr Trump entirely, a trial with major consequences for the 2024 election.

After a day of dramatic testimony, experts told the BBC it's still unclear who came out on top.

It's a "credibility contest" for the judge to decide who wins, said Atlanta defence attorney Andrew Fleischman. Mr Wade was nearly flawless in his well-rehearsed testimony, Mr Fleischman said, but Ms Willis' tone could put her at risk.

"Fani Willis's demeanour has been so extreme that that might incline him to disqualify her even if he is not sure of the other stuff," Mr Fleischman said.

Ms Willis will resume her testimony on Friday at 09:00 local time (14:00 GMT).