The frightening incident took place in Lidl in Devonshire Road at around 2.40pm yesterday (Monday, June 20), said police.
A boy, aged around 16, burst into the supermarket barefoot and was seen ‘running for his life’ down the aisles as the gang of thugs chased after him.
One mum shopping at the time said: “I’ve just witnessed the most terrifying thing you could imagine whilst shopping with my baby in Lidl.
“One young lad on his own, running barefoot around the shop screaming for help while being chased by a gang of lads wearing balaclavas with knives.
“Pushing everything and anyone out of their way in the process. My five-month-old nearly got thrown out of her pushchair.
"He ran into the stock room where they all caught up with him unfortunately.
"I’m not sure how he is. One of them dropped a knife on the way out and it wasn’t small.
"The sound is something that will honestly haunt me for the rest of my life.
"I’m shaken and it wasn’t even me. He was genuinely crying and pleading with them, hysterically begging for his life.
"He must have been 16, 17 at a push. He’s just someone’s child.”
The youths then fled the scene on electric bikes, according to witnesses.
Another customer who saw the incident unfold said the boy appeared OK afterwards and was kept safe in a store room until police arrived.
A police spokesman said: “We are aware and the matter is under investigation at this time.”