The so-far unnamed person was hit by a train between Moorgate and Finsbury Park, Thameslink tweeted. Their condition is not currently known.
It added: “All lines are blocked between these stations whilst the emergency services work to deal with this incident.”
Others reported seeing emergency services rush to the scene.
Writer and presenter Nicky Woolf tweeted: Anyone know what’s going on at Highbury and Islington station?
“It’s been evacuated for half an hour and there are like 15 emergency vehicles outside it.”
READ MORE: ‘Criminally stupid!’ Adonis savaged for claim UK will join Euro