Knife is pulled in robbery attempt.
She managed to raise the alarm by going inside the store and alerting security staff. When they came out, the man ran off towards the Lansbury Park area after threatening a man inside a Mercedes car with the knife.
Police say they are anxious to find the people who were threatened as they failed to make a complaint.
Security staff at the store reported the incident to the police.
Crime and Disorder Reduction Officer Andy Hillier, based at Bedwas police station, told the Echo: 'It could have been more serious than it was. We are grateful to security at Morrisons who acted quickly.
The man has been described as six foot tall or more, between 20 and 30 and was balding with white hair on the sides. He was wearing a grey hooded track suit type top with black jeans.
Anyone with information should contact Andy Hillier on 029 2085 7380.