More than 5,500 police will on duty for the G7 summit in Cornwall and the popular St Ives railway branch line will be closed, it has been confirmed.
Great Western Railway (GWR) said replacement buses would operate between main line station St Erth and St Ives from 7-14 June while the line is shut.
Roads in the area will also be closed, but police say they hope it will not be for longer than four days.
The summit is to take place from 11-13 June in Carbis Bay, near St Ives.
Media coverage of the event will be based in Falmouth.
The UK, US, Germany, France, Canada, Italy and Japan make up the G7 and leaders from Australia, India, South Korea and the EU will also attend as guests.
During a Facebook Live questions and answers session, Devon and Cornwall Police confirmed officers from across the country would be deployed.
Ch Supt Jim Pearce said: "We will be deploying over 5,500 officers and they will be in 100 accommodation bases."
He also said town centres would be "largely open", but the "closer you live to a venue, the more disruption there will be".
He added: "We're keen to keep roads open ... and hope not to have any closed for longer than four days."
The Cabinet Office has said it will be a "completely Covid-safe event" and "all delegates" will be tested and required to self-isolate if they are positive for coronavirus.
GWR said there would "some discomfort" with service changes which it hoped to keep "to a minimum" before they resumed as normal on 15 June.
Cornwall Council chief executive Kate Kennally also confirmed possible disruption around Cornwall Airport Newquay, but said security needed to be "robust enough".
She said staff were working to keep disruption "to a minimum" and "if it's a bins collection, a care worker's visit, it will still happen".
Ms Kennally added: "Our priority will be to support our residents."
The cost of the summit has not been revealed, but the Cabinet Office said central government will bear it.