The road remained closed to almost all traffic, with night cover erected over part of the scene, and was expected to remain closed at the scene where police tape stretched the width of the road.
The only exit for Mersey St workers east and south of the scene was a route through business properties, near a container park.
Well over 30 trucks had to be detoured past the Thames St entrance where drivers were told it was unclear when they would be able to access the area.
Staff arriving for late shifts at some of the premises in the area were also unable to get to work for much of the time, and among those unable to get back into the area were SPCA staff who had been out walking dogs when the incident happened.
A St John Ambulance spokeswoman said one ambulance and a rapid response vehicle were sent to the scene and transported the victim to Hawke's Bay Hospital in a critical condition.
Police said in a statement one person was allegedly assaulted by two other people.
The person has subsequently died.
"We are actively seeking witnesses to this incident," a police spokeswoman said, and door-to-door inquiries had been made at businesses throughout the area, including requests for CCTV images.
"Police believe this to be an isolated incident and are following strong lines of inquiry," the statement said.
The incident follows another serious assault in Hastings on Sunday. A man in his 20s remained on Monday morning in a critical condition after an apparent assault near a takeaway bar on Heretaunga St West, Stortford Lodge, about 1am on Sunday.
Anyone with information regarding the Pandora homicide is encouraged to call 0800555111 or 105 and quote file Number 210329/1374. This can be submitted anonymously.
