The freak weather sent stalls and their exhibits flying in the air during the Detling International Antiques and Collectors Fair, which attracted around 3,000 people.
"The tornado came out of nowhere," said Sue Ede, the director of the fair. "We were on the showground and a spiral of air about 50 to 60ft high suddenly whizzed straight through the middle of the exhibitors. It lasted for 30 to 40 seconds, but it seemed like two hours."
No one was injured, but many of the antiques were damaged. "It is not the kind of thing you expect on a beautiful sunny afternoon in Kent," she said. "The first thing I thought I saw was a parachutist in the sky, but then I realised it was part of a marquee flying off into the air."
The tornado came at them so quickly that the crowd had no time to panic or try to run away, she said. "People reacted in a typically British way afterwards and were worried about the person next to them, before starting to pick up the pieces of broken china and antiques around them."
Ms Ede said her team had now cleared the grounds ready for the second day of the fair today.
Summer was also put on hold elsewhere as thunderstorms brought mid-afternoon downpours to central London, East Anglia and the East Midlands.
Millions of Britons suffered in the sun as soaring temperatures caused widespread air pollution and holiday-makers sweltered in traffic jams.
Thousands of sun seekers were trapped on packed roads as the exodus to the South West caused queues of up to 15 miles on the M5 near Bristol.
Weathermen said blistering conditions country-wide produced the highest temperatures of the summer. Thermometers at Heathrow Airport reached 31C (88F) shortly after 1pm.
But accompanying high readings of ozone from London to Cardiff brought warnings from experts to asthma sufferers to stay indoors and seek medical help if they suffered extreme symptoms.
Hospital casualty units were expecting an increase in heat-related cases as experts warned patients who suffer from respiratory conditions to check medical equipment and take extra care during the hot weather.
Forecasters predicted the fine sunny weather would continue today with the prospect of isolated thundery showers this afternoon.