The co-owner of a restaurant in the Far North town of Russell says it was surreal that Justin Bieber gave an impromptu performance there.

The Canadian singer on Sunday posted a picture on social media of himself playing the piano inside the Duke of Marlborough Hotel.

Co-owner Anton Haagh told RNZ that Bieber, who wasn’t staying at the hotel itself, stopped in to the restaurant with seven others on Thursday afternoon.

"He was just after a few beers and some snacks, and he saw our red piano, and it's a baby grand piano in the corner, and he just jumped on and started knocking out a few tunes."

Haagh said Bieber had lifted the lid so the 50 people inside the restaurant could not see his face.

As for the set list, Haagh said Bieber did not play his own music.

"It was a lot of modern music, but he wasn't singing, he was just playing the piano."

The group had ordered seafood, including oysters and ika mata, along with beers and cocktails, Haagh said.

"It was really surreal sitting there.

"My daughter... we asked her to be the waitress, so she was absolutely fizzing, but managed to keep it together quite well."

As for the rest of the restaurant, Haagh said only four or five people had "clocked him".

"They'd gone to the toilet. As they walked past, they sort of went, 'Whoa,' turned around and went, 'Whoa.' And so, because he had this screen up, you couldn't really see his face from inside the bar.”

Haagh said the staff generally leave any "VIPs" alone and encouraged the rest of the restaurant to do so.

"I just made sure I asked everyone who clocked them, just, 'Hey, you can either spoil the moment and take photos and make a scene, or why don't you just sit down and just relax and enjoy it?'"

Haagh said the group left in "good timing" and missed the 30 to 40 people who had come in to see Bieber after word had spread.

He was not sure if the hotel would do anything to commemorate Bieber's visit.

 

"Normally, we just keep it quiet, but we're a bit amazed that he managed to post it on his Instagram, so, yeah, I'm not sure what we'll do with that, but we haven't really been in this situation before."