Hundreds of tourists had to be evacuated from Warwick Castle after a flaming cannonball set alight to a medieval thatched building during a display. Holidaymakers, many with young children enjoying the last day of the Easter break, had gathered to watch the cannonball be fired from the wooden trebuchet – the largest working siege machine in the world. However, the big display ended in catastrophe when sparks from the fireball ignited the roof of a nearby ancient boathouse, causing it to erupt into flames. The thatched building, which overlooks the River Avon within the castle grounds in Warwickshire, was unoccupied when it became engulfed in fire at about 5.45pm yesterday. Scroll down for video . Holidaymakers watched in horror as  a cannonball fired from a wooden trebuchet – the largest working siege machine in the world - struck a medieval thatched boathouse overlooking the River Avon at Warwick Castle . Witness Heather Taylor, 42, who had travelled from Birmingham with her six-year-old son Ethan to watch the cannonball launch, described the panic as the incident unfolded. She said: 'The trebuchet launched the flaming cannonball but as it flew almost over the boathouse sparks could clearly be seen coming off it and the high winds must have sent them onto the roof of the boathouse. 'There was a lot of panic and people were scrambling up the bank because they had no idea if the fire would spread. 'The place was packed with lots of young children and families. We were all evacuated and it was quite scary. 'It was shocking how fast the fire took hold. 'The cannonball actually appeared to land behind the boat house but it was obviously too close. 'It's such a shame because the boathouse has only just been re-thatched and we watched a chap thatching it before the big show. It's a medieval building so it's a big loss.' The catapult display ended in catastrophe when sparks from the cannonball ignited the roof of the ancient boathouse, causing it to erupt into flames at about 5.45pm. It forced an evacuated at the Warwick attraction . Video footage shows the medieval boathouse engulfed in flames after the flaming cannonball apparently set it alight yesterday afternoon. Warwick Castle said the attraction remains open today despite the incident . The thatched boathouse, which overlooks the River Avon within the castle grounds in Warwickshire (pictured above before the blaze), was unoccupied at the time and has now been completely destroyed by the flames . Up to 30 firefighters attended the incident and fire chiefs confirmed no one was injured by the blaze. The main castle was also unaffected by the fire. A Warwickshire Fire and Rescue Service spokesman said: 'We received a call at 5.47pm to a fire at the boathouse in the grounds of Warwick Castle. 'Three appliances were sent to the fire.' The historic boathouse, which was completely destroyed as a result of the fire, dates back to 1896. The 5th Earl, Frances Greville, had it built to house an electric boat which he powered by batteries charged from the electricity generated by the castle's mill. The trebuchet which fired the flaming cannonball stands 60ft high and weighs 22 tonnes. A flaming cannonball was launched from this wooden trebuchet, which stands 60ft high and weighs 22 tonnes, during a demonstration to show how the machine was used to hurl huge projectiles to breach the castle walls . The fire forced hundreds of tourists to be evacuated from Warwick Castle (above) at about 5.45pm yesterday . Warwick Castle confirmed the incident and said the attraction remains open and unaffected. A spokesman said: 'We did experience a fire in our boathouse yesterday which was safely extinguished within a short time. 'The island where the boathouse is located was not open to the public at the time and no-one was ever at any risk; nor did it affect any other part of the castle. 'We'd like to take this opportunity to thank Warwickshire Fire and Rescue Service for their prompt assistance. 'Despite speculation we have not yet ascertained the cause of the fire. A full investigation is underway. 'The castle will be fully open today featuring our spectacular Easter events programme.' The trebuchet, which is 60ft tall and weighs 22 tonnes, was used to hurl projectiles at the castle . The wooden trebuchet is the largest working siege machine in the world and is effectively a colossal catapult. It is a recreation of one of the biggest and most deadly military machines of all times, which was used as a weapon for protection. The trebuchet, which stands 60ft high and weighs 22 tonnes, was used to hurl huge projectiles to breach the castle walls. Large rocks and stones were the main ammunition but there is evidence of more unusual material used such as large flaming cannonballs. Manure and dead animals were also hurled by the machine into the besieged castle to spread disease, with pigs among the top choice of animals to be fired. The trebuchet at Warwick Castle is an authentic recreation by Dr Peter Vemming, from The Mediaeval Centre in Nykobing, Denmark. Notes and drawings from the 13th century were used as the starting point for the reconstruction and were often referred to during the process of developing the working replica of the powerful machine. The trebuchet, which was built at a workshop in Wiltshire, is made primarily of oak with the long throwing arm made of ash and metal fixings holding it together. - Warwick Castle .
Holidaymakers watched in horror as ancient boathouse erupted into flames.
Sparks from flaming cannonball fired from  wooden trebuchet caused blaze.
Tourists evacuated from Warwick Castle as thatched building burnt down.
No one injured in incident which occurred on last day of Easter holidays.