Bourges Boulevard has been re-opened following a carbon dioxide leak at Mcdonalds.
Emergency services were called at 1.40am today following reports of people feeling unwell.
It was initially thought to be a carbon monoxide leak - but emergency services have now confirmed it was a carbon dioxide leak.
A spokesman for Cambridgeshire police said the road was closed between the Mayors Walk junction and the Westfield Road junction while crews made the scene safe.
An East of England Ambulance Service spokesman said they had sent crews, but no-one had required treatment.
A Cambridgeshire Fire and Rescue spokesman said: “We currently have two fire engines at McDonalds on Bourges Boulevard, as well as two officers with hazardous materials training.
“The building has been evacuated and crews have identified a leak of carbon dioxide. This has been isolated and the building will soon be left with the occupiers.”
The fire service spokesman said there was no risk to public safety.