Peterborough Station is largely deserted with no trains running to London King's Cross.
The historic closure is due to work on the East Coast Upgrade, a £1.2 billion investment into the East Coast Main Line.
The lines between Peterborough and Cambridge and King’s Cross and London St Pancras International are closed for the first time in two decades both today (Saturday) and tomorrow.
The upgrade will deliver faster and more reliable journeys, more seats and more frequent services, rail chiefs claim.
There will also be a reduced service to King's Cross on Monday, so travellers are being urged not to travel as trains will be very busy.
Major upgrade work in the Newark area continues on Monday as well.
British Transport Police officers are at Peterborough Station today and are warning commuters that "journey times will be extended due to bus replacement services on most routes".