The Forestry Commission in Scotland is assessing the extent of the damage at 14 sites where infection has been confirmed, but says the number of trees needing to be destroyed could run into six figures.
The size of the problem emerged as UK Environment Secretary Owen Paterson said it would not be possible to eradicate the disease threatening to devastate the UK's ash trees.
But he raised hopes that trees could be found which were resistant to the fungus Chalara fraxinea, which causes the disease, and said it did not necessarily spell the end of the British ash.
Ash dieback has already led to 58,000 trees being cut down near Kilmacolm in Renfrewshire, and 30,000 being removed from a site in Scotland's north-east.
After another meeting of the Government's emergency committee on tackling ash dieback, it was revealed there are now 129 confirmed sites in the UK where the disease had been found.
The disease has killed up to 90% of ash trees in some parts of Denmark and is threatening Britain's 80 million ash trees.
A spokesman for the Forestry Commission in Scotland said it was difficult to put an exact figure on the number of trees likely to be cut down, but it could run into hundreds of thousands.
He said the commission's own site near Kilmacolm had been cleared of 58,000 trees, and added: "The other affected sites vary in size and how widespread the infection is, so it's hard to put an exact figure on it."
In an action plan published today, the Government rules out cutting down and burning mature ash trees to stop the disease.
Mature trees are valuable to wildlife, take longer to die and can help experts to learn more about genetic strains that could resist the disease, officials said.
The action plan will focus on tracing and destroying newly planted trees and those in nurseries, and better understanding the disease.
Mr Paterson said: "The scientific advice is that it won't be possible to eradicate this disease now that we have discovered it in mature trees in Great Britain.
"However, that does not necessarily mean the end of the British ash, if we can find those trees with genetic resistance to the disease and - restructure our woodlands to make them more resilient. If we know a small number of trees survived the intense epidemic in Denmark there must be hope here."
A summit of experts in forestry, environmental science and land-based industries, is to be held next week discuss the disease and future protection of Scotland's tree population.