There will be around three months of disruption while the old gas mains along South Street are replaced with plastic pipes.
The scheme will take place in four phases, with the top of South Street closed initially and buses rerouted.
Southern Gas Networks (SGN) say the essential network upgrade is taking place in January to minimise disruption – but some business have expressed concern.
Timpson is located between the Market Cross and Cooper Street, where the first phase road closure will be in place.
Employee Paul Taylor said: “Until it happens we won’t really know how bad it will be, but we’re worried about the loss of footfall.
“A colleague worked at a store where there were six months of road works outside and they lost a huge amount of customers.
“We understand it has to be done but no one wants it on their doorsteps.”
Rebecca Battersby, manager of nearby Seasalt, agreed. She said: “The loss of footfall could be the problem, and January is a quiet month anyway.
“I’m worried about access for our customers, it’s an incredibly important time coming up to the end of the (financial) year.”
Shelley Joel, assistant manager of Whirligig, added: “It’s going to be chaos, isn’t it?
“We’re right next to Cooper Street, so both the first two phases will impact on us.
“January is the perfect time to do it, but footfall is the major aspect for us. If they’re digging up the road people won’t want to come down this street.”
But the owner of Perfect Timing on South Street said: “I don’t see how it will affect us. If anything I’ll be delighted if there’s no buses going past us, they should be rerouted altogether.”
Phase two will see South Street closed between Cooper Street and West Pallant; phase three from West Pallant to Canon Lane; phase four from Canon Lane to Old Market Avenue.
The whole project should take around 12 weeks, SGN said.
SGN said the work was essential, that it would be the road, not the pavement, affected.
It was not made clear by SGN how the buses would be rerouted during the works, though the company said advance notice would be given.
Don’t miss out on all the latest breaking news where you live.
Here are four ways you can be sure you’ll be amongst the first to know what’s going on.
1) Make our website your homepage at www.chichester.co.uk/
2) Like our Facebook page at www.facebook.com/ChichesterObserver
3) Follow us on Twitter @Chiobserver
4) Register with us by clicking on ‘sign in’ (top right corner). You can then receive our daily newsletter AND add your point of view to stories that you read here.
And do share with your family and friends - so they don’t miss out!
The Chichester Observer - always the first with your local news.
Be part of it.