A 24-hour strike on Northern rail services has begun in a dispute over the role of guards on trains.
Members of the Rail, Maritime and Transport (RMT) union walked out at 00:01 BST over changes due to come into service in 2020.
Northern has warned travellers its routes would be "extremely busy" but said it expected to operate more than 40% of its normal timetable.
The action coincides with the first day of the Tour de Yorkshire cycle race.
The cycling event, which begins in Bridlington, East Yorkshire and finishes in Scarborough, North Yorkshire attracted more than a million spectators in 2016.
The row is over drivers being in charge of operating the doors, and guards being changed to on-board supervisors.
Arriva Rail North, which operates Northern, said very few trains would run outside 07:00 and 19:00 and urged passengers to check its strike timetable in order to plan their journeys.
It said it would also be running 300 additional replacement buses.
Both Transport for Greater Manchester and Transport for West Yorkshire warned of significant disruption.
The RMT has blamed Northern for the disruption after talks to avert the strike failed.
General Secretary Mick Cash said his members remained "united and determined".
The company said it was still prepared to talk with the union and said it was "disappointed" the strike was going ahead.
A protest by the RMT outside the Houses of Parliament on Wednesday marked one year since the union began its dispute with Southern Rail over the role of guards on trains.
Since then its members have taken 31 days of strike action involving a number of rail companies across England.