Great Western Railway have stated replacement buses will operate the main lines between St Erth and St Ives from 7th-14th June as the line closes for the G7 summit.
The high security event which is to be held in Cornwall this year, will involve over 5000 police and security forces. Though the summit is to take place from 11th-13th June in Carbis Bay, near St Ives, extra time and space will be needed to secure zones around locations involved in the summit.
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 be attending as guests.
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.
Devon and Cornwall Police said: "Cornwall hosting the 2021 G7 Summit will bring an inevitable level of disruption both regionally and locally.
"Devon & Cornwall Police are working with Government to minimize the impact on residents, businesses and visitors, as well as access restrictions to local services - particularly around the host venues in Carbis Bay, St Ives and Falmouth".
"We are keen to keep roads as open as possible and where routes are required to be closed, a traffic management plan that includes diversionary routes will be put in place".
GWR says full details of the replacement service will be available shortly and customers are being urged to check the website for future updates.