An estimated 20,000 people descended on the town of Buñol in the east of Spain on Wednesday for the annual La Tomatina tomato fight – often billed as the world’s largest food fight – to hurl tomatoes for an hour in a storm of pulp and crimson. Photograph: Alberto Saiz/AP

The tradition began in the mid-1940s, though its origins are unclear. The festival’s garish new official website attributes it to a foodfight that broke out in the town in 1945 during the ‘parade of giant heads’ and had to be broken up by the police. Photograph: Gustavo Grillo/Epa

The food fight was banned in the early 1950s until 1957 when the locals held a funeral for a giant tomato in protest, parading it around town in a coffin, and successfully had the ban repealed. Photograph: Alberto Saiz/AP

The town hall introduced a ticketing system in 2013, limiting the event’s attendance to 20,000 people. Photograph: Gustavo Grillo/EPA

Private tour companies sell tickets and accommodation in the nearby city of Valencia. Those willing to spend more can buy a coveted space on the back of the trucks that carry the tomatoes to the town, for an additional fee of €750. Photograph: Alberto Saiz/AP

Over 100 tonnes of tomatoes are brought to the town and thrown during the hour-long fight, at an estimated total cost of €140,000, or €2,300 a minute. Photograph: Alberto Saiz/AP

The tomato fight, which takes place every year on the last Wednesday of August, is the culmination of a week-long celebration made up of street parties, fireworks and food fairs. The night before the fight, participants compete in a paella cooking contest. Photograph: Alberto Saiz/AP

There are two signals for the food fight to begin: the firing of the water cannon and the first successful attempt to climb the Palo Jabón, a greasy pole with a piece of ham on top, and knock the ham off its perch. Photograph: Salva Garrigues/Demotix/Corbis

One tour website explains: ‘Technically the festival does not begin until one brave soul has climbed to the top of a two-story high, greased-up wooden pole and reached the coveted ham at the top. In practice this process takes a long time and the festival starts despite no one reaching the meaty prize.’ Photograph: Alberto Saiz/AP

In recent years the festival has become so popular that organisers have had to turn tens of thousands of people away. In 2012, an estimated 40,000 revellers – more than four times the town’s population – made the journey to Buñol to take part. Photograph: Gabriel Gallo/AFP/Getty Images

The fight begins at 11am with the firing of water cannon, and ends an hour later when they are fired again. According to the rules, participants must stop throwing tomatoes as soon as they hear the second round of cannon fire. Photograph: Gustavo Grillo/EPA

The tomato festival has become a global phenomenon, with copycat events staged at one time or another in Colombia, China, the US and Chile. The videogame Tekken 6 includes a battle arena based on the Tomatina, in which characters fight while surrounded by tomato-hurling revellers. Photograph: Gustavo Grillo/EPA

The clean-up begins in the afternoon, when fire engines move in to spray down the streets. According to one tour site: ‘Once the tomato pulp is flushed, the ground is clean due to the acidity of the tomato.’ Photograph: Alberto Saiz/AP