Part of Sherborne Road in Yeovil has been closed following a gas leak.
Engineers are hoping to complete emergency work on the A30 near the Pen Mill roundabout tonight.
A spokeswoman for Wales and West Utilities said: "We were alerted to the smell of gas this morning and immediately sent an engineer to investigate.
"Our engineer found gas leaking from a corroded gas pipe and is carrying out emergency repairs to this service.
"To enable the work to be carried out safely and quickly, one lane of the road leading up to the roundabout was closed."
If people smell gas they should call the national gas emergency number: 0800 111 999.