A gang of armed youths has terrorised employees and customers during a violent supermarket hold-up in Melbourne's outer south-east.

Footage obtained by 3AW shows a group of youths storming into the Lyndhurst Woolworths at Capital Promenade on Thompsons Road just before 9pm yesterday.

The group appears to make demands from staff, before counting back from five and then throwing bottles of soft drink across the counter.

Youths terrorise staff and customers at Woolies. (Nine)

Terrified employees can be seen screaming with their arms up in the air, as the offenders barge inside the store.

It is understood the youths turned violent when they were busted trying to leave the store without paying for a trolley full of items, including bottles of soft drink, lollies and sausages.

9News understands a woman was allegedly belted with a plastic bat near the cash register.

A witness named Rob told 3AW he saw the gang assault a female staff member while stealing a trolley of items.

"They elbowed her into the chest or neck and she fell back into the door," he said.

Rob said he ran after the youths, alongside two other customers, confronting them in the car park.

He said he punched three of the four offenders, who then threatened him with a kitchen knife after returning from a car.

"When I saw the lady get knocked over and how she was knocked over it turned something in my brain," he said.

"The one in front of me tried to hit me first, so I hit him back. I got hit from behind and then hit the other one back."

A Woolworths spokesman told 9news.com.au no staff members were injured in the incident and they were being offered counselling services.

The store went into lockdown during the incident until police arrived.

"There is no place for this aggression and violence anywhere in our community and our thoughts are with those caught up in the incident," he said.

"We thank our team for acting quickly to lock down the store in line with our safety procedures.

"We've been supporting Victoria Police with its investigations and will continue to help in any we can.

"We've also moved to strengthen the security presence at the store."

Victoria Police spokeswoman Belinda Batty said the armed group stole the trolley of goods.

"Police have been told a knife was produced and several customers attempted to intervene," she said.

"No one required medical treatment. The group left the scene in a vehicle and are yet to be located at this stage."

The group allegedly fled the scene in a Toyota Kluger.