A pair of robbers - one disguised in a shark onesie - have held up a petrol station in Canterbury early this morning.

Police say the two men threatened staff with a hammer and knife at the Rolleston BP on Main South Rd just before 2.30am.

Both hid their identities to carry out the early morning heist.

The second man was in a hoodie.

Police say the pair then stuffed a bag with lollies before taking off on foot.

Police say it was traumatic for the staff and they had to take refuge in another room.

They're being supported by Victim Support.

Police are going over security camera footage.