The store was closed on Friday afternoon
A three-year-old girl is in a critical condition in hospital after falling about 100ft (30m) from an escalator in Liverpool's Primark store.
The toddler was travelling up to the third floor with her family when she fell through a gap between the escalators to the lower ground floor.
She was taken to hospital where she is said to be suffering from broken bones and internal injuries.
The Church Street fashion store was closed after the incident.
The shutters of the shop were brought down on Friday afternoon as police and health and safety officers were called to investigate.
Merseyside Police said emergency services were called at about 1330 BST and the child was taken by ambulance to the Royal Liverpool University Hospital for treatment.
Officers spent the afternoon searching CCTV images and questioning staff and shoppers who may have seen the child fall.
A spokesman said an investigation was now being carried out by Liverpool City Council and the Health and Safety Executive.
A Primark spokesman said: "We are obviously profoundly shocked and saddened to learn of the accident in our Liverpool store this afternoon.
"We are doing all we can to assist the authorities in their investigation.
"All our thoughts are with the little girl and her family."
The discount fashion store, which at 84,000 sq ft is one of the biggest in the UK, opened last September after a major redevelopment of what had been a Littlewoods store.
It covers five floors and is even larger than the branch on London's Oxford Street.
On its opening day, eager shoppers queued around the block to be the first in and crash barriers were erected outside the building to avoid a scrum.