Canterbury businesses are being urged to be on the look out for suspicious activity following three robberies in the area.

The latest attack was on the Leithfield Hotel, 43km north of Christchurch, late on Saturday night.

A robber, wearing a balaclava and dark clothing, threatened the owner with a gun, tied him up and demanded keys to the hotel safe. He escaped out a window with an undisclosed amount of money.

Earlier in the day, a post shop in the Christchurch suburb of St Albans was held up by two men carrying firearms.

The men entered the Edgeware St shop about 12.30pm, demanding cash and then fleeing in a stolen 1992 blue Subaru Legacy.

The incidents follow a robbery on June 18, when two men stole thousands of dollars from the Avonhead Shopping Centre ANZ bank after handing a threatening note to a teller.

The men left the shopping centre in a silver Subaru Impreza, which was found abandoned in nearby Greendale Ave.

It was not clear if they were armed.

Detective Senior Sergeant Virginia Le Bas said police were investigating any possible connection between the robberies.

"It's a bit too early to say [if there is a link] until we've done a lot more work with witnesses and forensics, but the concern is that there have been two in 24 hours," she told The Press.

"There's a bit of work to be done looking at whether there are similarities."

Ms Le Bas warned shop and bank staff to be vigilant and ensure CCTV cameras were working.

"Anyone that anybody feels is acting suspiciously, around a bank for example, give the police a call so we can check it out."