A 30-year-old man from the Southport area was detained over the incident, which is believed to be domestic related.
A Tui spokeswoman said: “We regret to confirm that a female member of staff at our Southport Tui retail store tragically died in an incident today.
The 28-year-old victim was targeted on Saturday at the Tui branch in Southport, Merseyside, where it is understood she worked.
The woman’s next of kin have been informed, police added.
Police were called to the scene in Chapel Street at 1.25pm and the woman was taken to hospital, where she later died from her injuries.
“We’re doing everything possible to assist the local police with their investigation and support our customers and staff at this difficult time.”
A spokeswoman for Merseyside Police said: “We can confirm a murder investigation has been launched following an incident in Southport today.
A man has been arrested on suspicion of murder after a woman who was attacked at a travel agents died.