Detective Inspector Darryl Sweeney speaks on April 7 about a spate of aggravated robberies targeting bars in Canterbury. The robberies are a "serious spike in crime", he says.

An employee hid in a chiller fearing for his life after a robber blasted his way through the doors of a Christchurch bar with a gun.

Two weeks earlier the staffer, who works at Cashmere's Brickworks Bar and Restaurant and did not want to be named, was forced to the floor by a man who pointed a double-barrelled shotgun at his head.

The robberies are among five aggravated robberies targeting bars with a lone gunman in Christchurch this year. A team of 20 police officers, including a team of detectives, was formed on Thursday to catch those responsible.

GEORGE HEARD/FAIRFAX NZ The manager of Brickworks Bar and Restaurant says a man used a gun to blast his way into the bar on Wednesday night.

Detective Inspector Darryl Sweeney said there were some "commonalities" between the robberies.

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"Clearly there's a pattern . . . We see that as a series that needs addressing, whether they were all committed by the same persons that remains to be seen – certainly they've been observed as one set of offending."

GEORGE HEARD/FAIRFAX NZ It is the second robbery at the bar in 15 days.

There were six employees and several customers in the bar when the latest robbery unfolded about 9.45pm on Wednesday.

As has become custom since the March 15 robbery, staff had locked the front doors early because they were nervous they would be targeted again.

The bar's manager, who also did not want to be named, said a man came to the door with a gun and demanded to get in.

"He shot the front door in," she said.

"We just ducked and then we had to show ourselves because he was so angry. He was not happy because he wanted us to open it [the door]."

The employee said he and two colleagues dived into the chiller after hearing a gunshot and glass shattering.

He believed the man responsible was the same person who held a shotgun to his head and yelled at him to get on the ground two weeks earlier.

The bar manager said no-one was injured in Wednesday's robbery. The offender fled with cash.

She said her staff were already "on edge and paranoid" after the earlier robbery.

Wednesday's robbery was the fourth time a bar in Christchurch had been held-up this month.

Sweeney said police were "very concerned" about the spate of armed robberies.

"This is a serious spike in crime, it's not routine behaviour.

"We understand how distressing these events can be for the victims involved, and have offered them ongoing support and advice as we work through our investigations."

He said police were making "positive lines of inquiry" into the robberies.

Police would provide hotels and bars with help, including prevention advice.

The Tavern Harewood in Bishopdale was robbed by a man armed with a 12-gauge shotgun on March 11 as Lino Luafutu, the uncle of hip-hop artist Scribe, played a gig.

Luafutu noticed a security guard and a patron near the bar with their hands in the air and initially thought they were dancing.

The offender was chased from the bar by a security guard and a patron and dropped items related to the robbery, including some cash, while running through Bishopdale Park.

Police were also investigating the aggravated robbery of Trevino's Restaurant and Bar in Riccarton on March 24. It was understood the man had a weapon and stole cash.

Anyone with information on any of the robberies is asked to call Christchurch police on 03 363 7400. Information can also be provided anonymously by calling Crimestoppers on 0800 555 111.