They thronged the track to observe a minute’s silence at the Tamburello corner at 2.
17 p.m., the moment the Brazilian’s Williams ploughed into the wall while leading the 1994 San Marino Grand Prix.
Many carried flags and some pointed to the sky, as Senna did when he won, in remembrance before breaking into applause when the minute ended.
Austrian rookie Roland Ratzenberger had died the day before Senna” when he crashed during qualifying and the two remain the last driver fatalities during a grand prix weekend.
The circuit near Bologna was opened to the public with tribute events scheduled in Imola, including a memorial football match and the naming of a square, over the next four days. According to organisers, some 20,000 people attended on Thursday.
A mass, attended by Ratzenberger’s parents, was held on Wednesday night.
“It’s so emotional for us because it’s a long time and still the love from the people is very alive,” Senna’s niece Paula, representing the family, told Reuters Television.
“It seems like Ayrton is living inside people’s hearts, so it’s beautiful.”
Current Ferrari drivers Fernando Alonso and Kimi Raikkonen, as well as Senna’s friend and former McLaren team mate Gerhard Berger, were among those present at the track named after the late Enzo Ferrari and son Dino.
“For me he was an idol. I was a kid who rode karts, and back then I watched the news and saw that it was always him winning with his yellow helmet on,” said double world champion Alonso, who was 12 when Senna died. “That was what hit me the most.
“I had his poster on my wardrobe and it’s a shame that I never got to know him or race against him, but the number of people here at Imola… is a testament to his impact. He will always be immortal.”
Senna’s favourite Sao Paulo soccer team Corinthians donned replicas of his distinctive yellow, green and black helmet before the start of a Cup match against Nacional in Manaus on Wednesday.
Social media was flooded with tributes, recollections and an outpouring of affection for a driver held up as one of the greatest of champions, if not the greatest.
“He was the best and most charismatic race driver F1 has ever had,” said Austria’s triple champion Niki Lauda, now non-executive chairman of the Mercedes team. “He had personality, he was fast and he had charisma. No wonder that he won everything.”
Italian MotoGP great Valentino Rossi spoke on Twitter of Senna as “an inspiration, and even if 20 years have passed his spirit lives on in all racing riders and drivers.”
(Writing by Alan Baldwin in London, editing by Ed Osmond)