More than 40 firefighters took five hours to control a blaze at a barn that was engulfed by 40ft-high flames yesterday.

About 250 tonnes of straw and 120 tonnes of fertiliser went up in flames at the Redlands Dairy Unit, Hook Norton, north Oxfordshire, causing the closure of Sibford Road because of huge clouds of smoke.

About 50 heifers were inside the barn being milked and vaccinated when a farm worker noticed the blaze and raised the alarm at about 1.30pm. Staff moved in swiftly to evacuate the animals.

Station officer Gordon Macleod said: "The main problem was containing the fertilizer. The fire was melting the plastic bags it was contained in, then fertilizer poured out and fed the flames. We put precautions in to stop it exploding."

The cause of the blaze is not yet known, but it is not suspicious.