Two men were found injured on the tracks at a busy station causing severe delays for rail commuters.
British Transport Police (BTP) is investigating but said it was not yet clear how the men came to be on the railway line in an area at the north end of Birmingham New Street station today.
The incident caused disruption to services in and out of the station from 6am.
A police spokesman said: "Officers from BTP West Midlands attended Birmingham New Street station after reports of two men on the railway line. Words:PA
"Medics attended and administered first aid to the men at the scene."
He added: "At this time it is unclear how the men suffered their injuries and the incident is being treated as unexplained, while officers continue inquiries and establish the full facts as to how the men came to be on the tracks."
The police have urged anyone with information to call on 0800 405040.
The incident meant some Arriva Trains Wales, CrossCountry and London Midland rail services were running with delays up to 20 minutes, according to National Rail Enquiries.
Network Rail said normal running had resumed but cautioned rail passengers to expect some residual delays between Birmingham and Wolverhampton.
The UK's worst train stations
Trains delayed by injured men on tracks in Birmingham
This Edwardian station was built in the early 1900s and is operated by East Midlands Trains. 59 per cent of people surveyed said they were satisfied with the station - a low score which ranked it bottom for both cleanliness and facilities in the Passenger Focus National Passenger survey.
Birmingham New Street railway station is the largest and busiest serving Birmingham. Despite the regular flow of people, only 64% of passengers surveyed in the National Rail Passenger Survey (NRPS) are satisfied with the sation.
London Bridge railway station is a central London railway station and a London Underground complex in the London Borough of Southwark. The station is the oldest railway station in central London and one of the oldest in the world. 67% of passengers surveyed were satisfied with this station, the fourth busiest station in London.
Peterborough railway station is a major interchange serving both the north-south ECML, as well as East-West long-distance and local services. The station is managed by East Coast. Just 67% of passengers surveyed were satisfied with this station.
Crewe station was completed in 1837 and is one of the most historic railway stations in the world. Like London Bridge and Peterborough, only 67% of passengeres surveyed were happy with this station.
Gatwick Airport station provides a direct rail connection to London. The station platforms are located about 70 metres away from the airport's South Terminal. 69% of passengers surveyed were satisfied with this station.
Stockport railway station was identified as one of the ten worst category B interchange stations by a mystery shopper assessment in 2009. Despite improvements being made to the station since, it is still one of the ten worst stations with only 70% of passengers satisfied with the station.
Clapham Junction station is one of the busiest in Europe by number of trains using it with many routes from London's two busiest termini, London Waterloo and London Victoria. Only 71% of passengers surveyed were satisfied with this busy station.
Maidenhead railway station serves the town of Maidenhead, Berkshire, England. It is served by local services operated by First Great Western from London Paddington to Reading, and is also the junction for the Marlow Branch Line. The survey showed 71 per cent of respondents were satisfied with the overall quality of the station, giving it the ninth lowest satisfaction rating.
Coventry station has the PlusBus scheme where train and bus tickets can be bought together at a saving. Despite this convenient feature, only 72% of passengers surveyed were satisfied with the station.