HUGE hailstones bigger than grapes battered Oxford in a freak downpour, smashing glass, setting off car alarms and forcing people to run for safety.

Thunder roared across the sky this afternoon before the massive chunks of ice pelted the ground, in tune with the Met Office's yellow weather warning which came into effect at 11am.

Derek Holmes in Bayworth near Boars Hill was "shocked" when he headed to his garden to get tomatoes for lunch, only to find that the stones had smashed his greenhouse. 

Oxford Mail:

The 53-year-old editor and writer said: "It shows how big the hailstones were and how violent the storm was, it was incredible.

"I was shocked to see it had put a hole in the pane. We have got a conservatory with a plastic roof and it was hammering on that, it was extraordinary.

"They were certainly the size of large marbles and my neighbour's had one the size of a golf ball."

Lucy Bickerton tweeted that the torrential downpour set off a car alarm near her:

Others tweeted pictures of the hailstones as wide as two pence pieces.

Richard Holmes in Abingdon shared a picture of a stone just slightly smaller than a ping pong ball:

Oxford Mail:

Jackie Simmons in North Oxford shared a picture of her porch flooded with rain and hail:

Oxford Mail:

Malgorzata Gosia Nowakowska sent us this incredible shot of gnarled and nodular hailstones in Bicester: 

Oxford Mail:

Paul Lowe, in Boars Hill, submitted a fantastic photo of them piled up on grass: 

Oxford Mail:

The Met Office said Oxfordshire could experience "torrential downpours" today, which are expected to ease later on before more rain sets in tomorrow.

Familes at the Big Feastival near Chipping Norton will have to battle the elements to avoid getting soggy burger buns, with heavy rain expected to lash down from 2-3pm. 

Chief forecaster for the Met Office Eddie Carroll yesterday told the Oxford Mail there was "a risk of some locally large rainfall totals" from 25 to 50 mm. 

The warning is in place until 9pm tonight.