More than 100 staff successfully participated in a test of the major incident plan at Croydon University Hospital.
The exercise, which was facilitated by an external team, was held to test the system currently in place to deal with major emergencies.
Staff from community and hospital teams were told there had been a major rail crash at East Croydon station involving the Gatwick Express.
Within minutes, the seriously injured and walking wounded were being brought from the scene to the hospital's accident and emergency department.
Richard Parker, director of operations, led the Incident Control Team through the test.
He said: "The energy and activity in the rooms set aside for this real-time test were amazing.
"Even though it was a "table-top" exercise with no real casualties everyone went into action as if it was actually happening."
The trust's emergency planning manager, Mike Hayward, said: "The teams worked very well and were able to go from a normal working day to a major incident status within a matter of minutes.
"Our plan was tested and came through with flying colours, but the whole point of carrying out exercises like this is to fine-tune every aspect and there are always things that can be improved, and that is exactly what we will do."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here