Four fire engines have been sent to a fire at the old planning offices at South Hill.
A total of 18 firefighters are on the scene in St Helier this afternoon (3 January).
An Incident Command Vehicle and Fire Duty Manager have also been dispatched.
The fire is said to be on the first floor of the former offices.
Footage posted online shows smoke coming from the building.
People are being asked to avoid South Hill, as the road is closed at both ends.

Opponents ask if St Mary solar plans have been 'abandoned'
Jersey takes step closer to protecting whistleblowers
Tickets on sale for women's Muratti
New 'competitiveness' plan to protect Jersey's £3bn financial sector
Fines for 'Jersey Lifts' drivers a step closer?
£225K grant given for clinical trial into heart failure
New school grouping system to address pressures on Education
Jersey to nearly quadruple its protected waters