Police and traffic authorities are preparing for a potential exodus of residents leaving the Blue Mountains before an extreme fire danger sets in.
The Rural Fire Service (RFS) has urged any residents without an important reason to stay in the Blue Mountains to leave before lunchtime on Wednesday.
As a result authorities will be keeping an eye on traffic congestion.
"The police and management services team are aware of that," RFS Commissioner Shane Fitzsimmons said.
"We are encouraging people not to travel through the Blue Mountains tomorrow unless they really need to.
"Reconsider travel plans."
NSW Police have also urged heavy vehicles to avoid non-critical travel on the Great Western Highway between Penrith and Lithgow as conditions could worsen with little notice.Long and wide load permits have also been revoked.