Twenty firefighters tackled a blaze this morning on the old Radcliffe Infirmary site where Oxford University’s new £500m campus is being built.

Fire crews were called to Walton Street, opposite Oxford University Press, shortly after 8am to tackle the flames, after a building under demolition caught fire.

The street was cordoned off for a time as firefighters used three engines, including a hydraulic platform, to bring the fire under control.

Incident commander Rob MacDougall said the fire started after polystyrene insulation boards caught fire.

He added: “There were about 12 construction workers on site at the time and they tried to put out the flames, but the polystyrene caught light very quickly, so they did the right thing and called us.

“This was an accidental fire, and no-one was in any danger at any point. We shut Walton Street so we could bring in our hydraulic platform, which we used to carry out an inspection from above.

“If the fire had spread, we would have been able to use the platform as a water tower.

“Staff at Oxford University Press were asked to use their front entrance instead of the side entrance in Great Clarendon Street while we were dealing with the fire.”

Tom Howard, 21, who is studying theology at St Benet’s Hall, returned home from a night away to find fire engines were blocking a path to his home off Walton Street.

He said: “I had to take a small diversion. When I saw all the fire engines I thought it was a big fire, but I’m relieved to hear it is not too serious.”

The Radcliffe Infirmary site was bought by Oxford University in 2003 and a £500m city centre campus is being built between Walton Street and Woodstock Road, with the first new buildings expected to open in 2011.

Oxford University has not yet issued a statement about the fire.

A spokesman for Oxfordshire fire and rescue service said firefighters were still at the scene at 10.30am and could not say when Walton Street would reopen to traffic.