Event commissioner Giuseppe Sala also delivered an upbeat report on construction work for the six-month extravaganza with all but two of the giant pavilions on the 110-hectare site in the suburbs of Italy's industrial hub on schedule.
In the aftermath of the recent attacks in Paris, Sala revealed that the installations would be protected by airport-style security with a perimeter fence, scanners and some 2,000 cameras.
"I will not dramatize it, but it is an event that could be subject to risks," he said in a briefing for international media.
Of the tickets sold, five million have been bought outside Italy with China having snapped up a total of one million.
"When you think that between 800,000 and 900,000 Chinese visit Italy per year... we are going to bring in one million in six months," Sala said.
Italy is counting on the food-themed fair to help lift a moribund economy out of the doldrums, as well as showcasing the country's capacity for innovation and its openness to investors.
Sala said it was difficult to assess how much the Expo would add to growth but nevertheless predicted "added value" for Italy of €10 billion - €5 billion for tourism and €5 billion in other economic benefits.