A routine grocery shop took a shocking turn for a Townsville couple who were confronted by a masked man with a concealed weapon.

Isabella King and her boyfriend were taking groceries to their car at CastleTown Shoppingworld this afternoon when two people walked past them in the carpark wearing skull face masks.

Ms King said the pair did something strange before her and her partner were confronted.

"A guy and a girl who were wearing skeleton face masks came up past us and were barking like a dog," she said.

Ms King spoke to her partner briefly about the interaction before they got in the car ready to drive off.

"The person turned around and started waving their arms around so my partner hopped out of the car," she said.

Ms King said her partner tried to reason with the man but it did not work.

"The guy pulled a knife or a weapon wrapped in a cloth from his pants … the guy then laughed and put the weapon back into his pants and walked off with the girl," she said.

They notified security about the incident who called police.

Queensland Police confirmed they were called to the centre about 3.20pm but could not find anyone responsible.

Ms King said the masked people could have been teenagers and wanted to make sure other shoppers were aware.