A man brandishing a knife slashed himself across the throat in a Cornish town's Woolworths store.
Woolworths has offered counselling to Penzance staff
Penzance shoppers fled in panic as the man entered the store at about 1500 BST on Thursday.
An ambulance service spokesman said the 23-year-old local man died within minutes after sustaining self-inflicted arm and throat injuries.
A police spokesman called it "horrific for everyone watching". Nobody else was involved in the incident.
Died 'in minutes'
According to a South West Ambulance spokesman the man entered the store and began walking up and down the aisles waving the knife about.
Woolworths staff quickly cleared customers from the shop and alerted the police and ambulance services.
By the time an ambulance crew arrived at the scene, the man had slashed his throat and had already died.
The ambulance spokesman added said: "Unfortunately the man died within minutes."
A spokeswoman for Woolworths said the store would remain closed on Friday.
She said: "Yesterday's events were extremely disturbing for our colleagues and our priority now is to ensure their welfare and we are supporting them in every way possible.
"We will only reopen the store when we feel it is right to do so and our staff will have our ongoing support."