Patrons sheltered under tables fearing for their lives as two masked men shot up a North Shore pub before robbing the bar.

A witness said about 10pm last night two masked men dressed in black head to toe, one carrying a semi-automatic shotgun, "swaggered" into the Good Home gastropub in Birkenhead.

The bar was closing after the All Blacks game ended, but there were about 30 people remaining, he said.

"These guys walked in with a swagger. They were calm and collected. They knew what they were doing, knew where the safes were."

Terrified patrons sought shelter under tables as one of the men pointed the gun at bar staff.

Two older patrons attempted to intervene.

"They tried to fight [the masked men]. I basically witnessed one of them put a gun to his head, before letting a warning shot off. I thought, 'Mate these guys aren't joking'. They weren't blanks, there was a hole in the ceiling. It was nuts.

"He then bashed the guy who was trying to fight one of them over the head with the butt of the gun, cracking his head open. Then he fired another warning shot.

"Everybody in the bar was yelling and screaming. We were telling these guys just to leave them alone. I thought somebody was going to be killed."

They were big guys, about six foot three inches, he said.

They didn't appear to be on drugs.

"They were just so calm. They looked like they had done this before. If they were on drugs, I think somebody would have been killed."

The witness said he was good friends with the staff, who were "pretty shaken up".

"It was all females on last night. Most of them are pretty shaken up. These guys were cowards."

He was not sure exactly what was stolen, but believed the robbers took some money.

They made off in a white Subaru Impreza WRX with black mags, he said.

It was the second armed robbery this year at the pub.

In January two men disguised with balaclavas and carrying weapons, including a gun, entered the pub before stealing cash and making off in a stolen car.

"I am pretty angry," the witness said.

"They got robbed six months ago, and then this happened right in front of us. It is f****** horrible."

Detective Senior Sergeant Jason McIntosh said an investigation into the incident was under way.

An as yet unknown quantity of cash was taken, he said.

The white Subaru was recovered a short distance away in Roseberry Ave, Birkenhead.

The bar was closed and a scene examination was under way.

CCTV footage was being examined and police are speaking to witnesses and patrons.

Anyone with any information is encouraged to contact the Waitematā District Crime Squad on 09 839 0697.

A St John spokeswoman said they attended the incident shortly after 10pm.

One person was treated for minor injuries.