A south London train line was closed after police responded to a concern for welfare at Catford Bridge railway station on Friday afternoon.
Southeastern and Network Rail warned passengers of delays on the line from Lewisham to Hayes after the incident and by 3pm a normal service had resumed.
The British Transport Police said: “Officers were called to Catford Bridge railway station shortly after 1pm on today following reports of a concern for welfare.
“Officers attended along with the ambulance service and the person was taken to hospital.”
London Ambulance Service also sent a crew to the site.
Elsewhere, hundreds of Border Force officers at Heathrow Airport started a three-day strike on Friday in a dispute over rosters.
The Public and Commercial Services union (PCS) said more than 500 of its members working on passport control at terminals 2, 3, 4 and 5 are taking action in protest at new rosters being imposed.
The strikes will be followed by three weeks of industrial action short of a strike, including a ban on overtime.
The union said it expected disruption over the weekend as families return to the UK at the end of the half-term holiday.
A Home Office spokesperson said: "Border Force have robust plans to minimise disruption and keep the border safe and secure.
"We recommend that passengers check the latest advice from their operators before travelling."
Meanwhile a multi-vehicle crash on the M25 had stopped traffic between Junction 6 Godstone and Junction 5. Traffic is now moving along the section after delays of around 90 minutes for some motorists.
