A "once in a lifetime" Olympic Torch tourism boost could pump an extra £7 million into the Cornish economy in a few days and have an impact lasting many years to come.
According to industry leaders, the Olympic Flame relay starting in Cornwall and showcasing the county to the world will have an impact "beyond value".
Lady Cobham, chairman of VisitEngland, said it was a golden opportunity.
"Over the next 48 hours, the eyes of the world will absolutely be on Cornwall.
"It is an iconic moment for the world and it is a wonderful moment for Cornwall."
Malcom Bell, chief executive of VisitCornwall, said the fact that the torch arrived in the county – and that it was the scene of the start of the 70-day tour – were among the most important events of the entire Games.
"It is a dream ticket," he said.
"There is not a destination in the world that wouldn't drool at the prospect of getting the first day of the Olympic Torch relay on their patch.
"The fact is that there are only two days that count – day one and day 70 and we know where they both are."
VisitEngland, the national tourism body, was said it was too early to say what the effects of the relay would be on a regional level.
Lady Cobham told the Western Morning News that although it could not put a number to it, the widespread belief was the effect would be enduring.
Mr Bell said VisitCornwall's early analysis suggested that the immediate boost would be between £5 million and £7 million, with much of that concentrated in the west of the county, scene of the flame landing at RNAS Culdrose near Helston last night and the relay start.
"We have got lots of VIPs and journalists from all over the world and I think most of West Cornwall is pretty booked up," he said.
"On the route itself, we have people travelling down to see key moments and we have people out for the day watching it and spending money. We believe it's worth between £5 million and £7 million.
"The thing with tourism is to reach markets that we would not normally get to.
"It's estimated that up to one billion people will be watching what's happening. They will see Cornwall looking spectacular and attractive."
Among TV crews in the county is one from China, which is syndicating coverage to 20 networks, a team from Japan sending material to five networks, and crews from Mexico, Australia and other countries. Mr Bell said the crews had already spent time filming at some of Cornwall's iconic locations, such as St Michael's Mount.
"You can't buy that kind of advertising," he added.
"The direct benefits are not to be sneezed at, but the indirect benefits of putting Cornwall on the map around the world are beyond value."