Mannings on Wednesday said it is highly concerned about an incident where a customer was believed to be wrongly accused of theft and mistreated by security guards.

In a social media post on Tuesday, a woman said she was accused of theft after buying two boxes of cough syrup at a Mannings branch in Tsim Sha Tsui.

According to the post, she paid for the items at a self-checkout counter, but was allegedly grabbed by the neck by two plain clothes security guards and dragged back into the store.

In a statement, Mannings apologised to the customer and said the security guards were from a third-party company.

The chain store said the guards had been fired and that it had ended its contract with the security company.

"At the same time, we have established a task force to follow up on the incident, including reviewing store security and related processes to prevent similar incidents from happening again," the statement read.