Rail bosses have warned of "catastrophic" consequences of railway trespass as shocking new images of young people on the railways were released.
In one incident two boys were caught on camera walking along rail tracks near Crawley where trains reach speeds of 85 mph.
Another CCTV image showed a teenager lying on a level crossing near Tunbridge Wells while using her phone.
Network Rail warned that young people often "don't understand that tracks are live at all times."
The images were released by Network Rail as recent figures showed a shocking 40% rise in youth trespass in South East London, Surrey and Sussex as the first lockdown lifted.
Trains travelling at high speed take hundreds of metres to stop and rail bosses said it was important everyone understood the dangers of trespassing.
Nicola Dooris, community safety manager on the South East route, said: “Unfortunately, during lockdown we have seen an increase in the numbers of young people messing about on the railway.
“On that section of track, trains often travel at 85mph and, at that speed, unlike cars, trains can take hundreds of metres to stop – a fact many young people don’t realise.
“Using CCTV like this, I’m often able to track down young people and talk to them, and I’d much rather do that than help our staff cope with the aftermath of young people being killed.”
The children, whose identities have been disguised in the CCTV pictures, have been spoken to by transport police officers, Network Rail said.