Jodi McKay secures leadership of the NSW Labor Party - The Age

Ms McKay and Mr Minns endured an hours-long wait for the verdict, as Labor scrutineers and officials spent most of the day verifying the rank-and-file ballots against party membership lists.

It is the first time the process has been used to elect the NSW Labor leader, under the same rules introduced by former Labor Prime Minister Kevin Rudd in 2013.

Despite the delay, the day was not without drama, with tensions boiling over earlier in the morning as the caucus vote was underway inside Labor's party room at NSW Parliament House.

Outside the caucus room, and in full view of the assembled media, Bankstown MP Tania Mihailuk accused upper house MLC Mark Buttigieg of "standing over" Shellharbour MP Anna Watson while the vote was taking place.

Kogarah MP Chris Minns put up a tough fight.Credit:AAP

In an exchange heard by journalists standing 20 metres away, Ms Mihailuk yelled at Mr Buttigieg: "Don't stand over a woman".

Mr Buttigieg responded, yelling: "Don't try that sh*t on with me, Tania."

Both MPs gave differing accounts of the incident moments earlier inside the caucus room that led to their heated hallway clash.

Mr Buttigieg - who voted for Ms McKay - claimed he had a "pre-existing pairing arrangement" with Ms Watson in which they agreed to show each other their votes, and denied there was any attempt to intimidate her.

"I literally walked over to her and showed her my vote. I leaned over to show her my ballot paper and I looked at hers," he said.

Ms Watson, who entered the caucus room with Mr Minns and his supporters, declined to comment, telling the Herald: "I don't talk about what happens in the caucus room".

Ms Mihailuk, who backed Mr Minns, claimed she watched Mr Buttigieg "fully standing over" Ms Watson in an attempt to see which way she was voting.

"There's no way that's a normal pairing arrangement. He was fully standing over her. She was sitting on the lounge and he was standing right on top her," she said.

"[Ms Watson] looked really intimidated to me. I checked if she was okay, and she said she wasn't okay."

Ms Watson confirmed Ms Mihailuk had inquired after her wellbeing, and said she left the party room shortly after she cast her vote to return home to care for an ill family member.

Auburn MP Lynda Voltz, who was sitting next Ms Watson in the caucus room, said she didn't see anything unusual in the interaction between Mr Buttigieg and Ms Watson.

"I was sitting next to Anna and if she was being intimidated, I would've noticed," Ms Voltz said. "She certainly wasn't."

Ms McKay's election will trigger a fresh round of internal campaigning, which will begin almost immediately as MPs start jostling for front bench positions.

Acting leader Penny Sharpe will face a challenge to the deputy role next week.Credit:AAP

Her victory will also be a factor in determining the deputy leadership position, which will be elected by the caucus at another meeting on Tuesday.

Swansea MP Yasmin Catley, Ms McKay's chief lieutenant during the leadership campaign, is expected to challenge acting leader Penny Sharpe for the role, in a move that will split the party's Left faction.

Another of Ms McKay's key backers, Adam Searle, is expected to retain his position as the party's leader in the upper house. But Walt Secord, a key supporter of Mr Minns, could struggle to hold onto his position as deputy leader in the upper house.