The NRL has threatened to ban spectators who threw projectiles at referee Ashley Klein, with the league's integrity unit investigating the aftermath of Sunday's semifinal in Auckland.

Footage from after full-time in Newcastle's 12-10 win over the Warriors at Eden Park showed a raft of bottles, cups and rubbish being thrown at Klein as he walked from the field.

Klein had to be protected by security as fans abused the veteran referee and threw projectiles.

The NRL immediately launched an investigation into potential breaches of its spectators' code of conduct.

An integrity unit investigator had been at the ground.

"If found guilty, they [the fans] will be banned for a period of time from attending NRL games," ARL Commission chair Peter V'landys said.

Auckland police have since confirmed no arrests were made.

They said there were "no issues to note", other than two pitch invaders.

Sunday's crowd of 48,511 marked the largest ever for a rugby league match in New Zealand, after the NRL made the call to move the match from Mount Smart Stadium.

The spectator abuse came after two contentious calls went against the Warriors late in the match, including a decision not to penalise Tyson Frizell for an escort in the dying minutes.

Warriors great Shaun Johnson hit out at the response of spectators after the match, labelling it "embarrassing".

"It leaves a bit of a sour taste in your mouth [after] what has been an unbelievable night with the colours, the energy, the happiness and celebration," Johnson said on Sky NZ's coverage.

"But there is just no need for it. It's just embarrassing.

"Ashley Klein has probably refereed the best game of rugby league I have seen in a long time tonight.

"He didn't take any gamesmanship in terms of people laying down. He didn't let people approach him whingeing.

"He didn't make the game about him. He let the players come and play and they dictated the outcome."

Warriors coach Andrew Webster vented his frustration in the post-match media conference, highlighting a bunker strip call on Te Maire Martin and the decision not to penalise Frizell for a possible escort on Leka Halasima.

"The last one, [when] two points would have drawn the game, he [Frizell] is going across Leka, pretending to try and catch the ball, which they've told us you can't do," Webster said.

The incident came after AFL umpires also had bottles and cans thrown at them while leaving the MCG following Hawthorn's nine-point loss to the Brisbane Lions in Saturday night's preliminary final.

The AFL has condemned the behaviour and warned of minimum five-year bans for any fans found responsible.

AAP