A terrified shop worker was threatened with a knife by robbers yesterday afternoon.

The two men waited until the youth had opened his till at Bell's store, on the Red Hall estate, in Darlington, before holding up a knife and stealing a quantity of bank notes.

The incident was the second knifepoint robbery in as many days in the town.

On Thursday evening, two female workers, in their early 20s, at Ken Warne's supermarket, in Cleveland Terrace, were confronted by two men, one of whom had a knife.

The pair waited until the store was empty before one guarded the door and the other grabbed money from the till.

Police believe the two incidents could be linked.

Detective Sergeant Dave Wilkes, of Darlington police, said: "It is a concern that these incidents are happening, but this is not an epidemic.

"We believe it is opportunist. They are trying to grab money where they can but there has been no physical violence sustained by any member of staff."

Yesterday's incident happened at 12.45pm at the shop in White Hart Crescent.

The men did not speak but one held up a knife in his hand. They fled in a red car.

Det Sgt Wilkes said the till worker, in his late teens, was left "absolutely petrified".

Thursday's incident happened at 9.20pm. The robbers again did not speak but pretended to buy confectionery before stealing cash.

Manageress Jan Rogers said the men were caught on security cameras. "They didn't get much but the staff members were left shaken," she said.

The men involved in Thursday's attack were white and about 5ft 7in or 8in.

One was wearing a scruffy blue baseball cap and dark denim jeans.

The other had light brown hair and was wearing a Burberry-style checked shirt.

Anyone with information should call Darlington CID on (01325) 742111.