Staff shortages due to timetable changes have been blamed for train cancellations, with passengers warned more could follow.

Transport for Wales (TfW) has blamed work on the new timetable, which came into force on Sunday.

This led to 12 train services being cancelled before 13:00 GMT and delays.

TfW apologised and thanked workers who had given up rest days or volunteered to work overtime.

Earlier TfW's website showed there were delays to services between Aberystwyth and Shrewsbury, from Cardiff to Shrewsbury and Swansea and Chester to Holyhead, among others.

A bus replacement service was also operating between Llandudno and Blaenau Ffestiniog.

Rail users took to social media to complain about missing connections as a result of cancellations or trains being full because of issues.

"We're sorry that there have been a number of cancellations on our network today," a TfW spokesman said.

"As always, we are very grateful to colleagues who gave up their own time to volunteer to work overtime and rest days."

TfW said over the past few months it had been "meticulously planning and preparing" for the new timetable by recruiting additional staff.

Capacity is being added for 6,500 more Valley Lines passengers, while an extra 186 Sunday services will also be added in Wales.

The spokesman added: "We are continuing to do everything possible to ensure the maximum number of services are operating every day and this time of year can always be challenging, particularly on weekends."

TfW runs hundreds of services each day across Wales and some running over the border into England.