A statement from Merseyside Police on Saturday said: 'Merseyside Police can confirm a murder investigation has been launched following an incident in Southport today. Iv not worked for Tui for a while but the time I did and worked with Cassie she was such a lovely girl.
Two air ambulances were also flown nearby to the scene as police cordoned off the area - and a huge crowd of shoppers gathered to watch the drama.
She was transferred to Southport Hospital where she later died.
Cassie Hayes, 28, was targeted as she worked her shift at the travel agent in Southport town centre on Saturday, with officers from Merseyside Police called to the scene in Chapel Street at 1.25pm. The incident is believed to be domestic-related.
Ms Hayes was "well-known" to many people in the travel industry, according to a fundraising page set up in her memory by other travel agent workers.
"We're doing everything possible to assist the local police with their investigation and support our customers and staff at this hard time". "I was further down Chapel Street and didn't hear any gunshot".
Delivery driver Rich Lawson, 27, was dropping off a package at the nearby Vision Express shop when he said he was ushered in and locked inside by staff.
Police later confirmed a 30-year-old man is in custody.
She posted: "What can I say".
He said: "When I got there they had locked all the doors".
"'She was covered up but I could see blood on her face".
Detectives are appealing for anyone with information to contact Merseyside Police on 101 quoting log 470 of 13 January or the Crimestoppers line anonymously on 0800 555 111.