Trains between Reading and Didcot Parkway are facing delays after a suspected trespass incident blocked the line near Goring and Streatley.
In a statement online, a spokesperson from National Rail said there had been "major disruption" between Reading, Swindon, and Oxford, with delays expected until 7pm.
An update from Great Western Railway at 6.45pm announced that all lines have now reopened following the emergency.
Passengers have contacted The Reading Chronicle to say that some services had to reverse back to Didcot due to the obstruction.
CrossCountry routes were affected between Bournemouth and Manchester Piccadilly and also between Reading and Birmingham New Street and Newcastle.
Great Western Railway routes were affected between London Paddington and Didcot Parkway, Oxford, Banbury, Cheltenham Spa, Worcester Foregate Street, Bristol Parkway , Bristol Temple Meads, Weston-super-Mare, Taunton, Great Malvern, Hereford, Cardiff Central, Swansea and Carmarthen.
Chiltern Railways and South Western Railway are conveying passengers via any reasonable route until further notice.
Arrangements have been made for Great Western Railway rail tickets to be accepted for these journeys.
The emergency services have been contacted for further information.
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