National Rail said passengers should expect delays until about noon and it is believed the incident has happened near Conisbrough. The nature of the incident has not yet been stated.
A spokesperson added: "Emergency services are dealing with an incident between Swinton and Doncaster, closing all lines.
"Trains are currently unable to run between Sheffield and Doncaster. Buses have been requested, however there is no estimate as to when they will be in place."