The Labour MP told workers at the station, opposite the Palace of Westminster, that they needed to open the doors and get people out as quickly as possible.
During an interview with BBC news, she said she saw people running towards her as she got off an escalator in the station.
She said Portsmouth MP Penny Mordaunt shouted: “There’s shots being fired, we need to get out of this place.”
Ms Creagh said: “I turned around, the escalators were on the down, we couldn’t get back up.
“We had no choice but to go out of revolving doors one at a time and that’s when I shouted to the security guard ‘you have got to open these doors, we have got to get out of the building now’.”
Ms Creagh then called on controllers to shut the tube station completely to try and keep people out of danger.
She told the BBC: “I thought to myself actually the one thing we don’t want is a load of tourists walking up and wandering in with their children into this situation.
“I went to the control room and I told the controller that there had been what we thought was a terror attack on the Palace of Westminster.
“I said we have got to shut the station now, we have got to stop people coming into this situation.”
Asked if she was able to convince people that she knew what she was talking about, the shaken MP replied: “I didn’t have my badge on, I didn’t have anything. I just had the authority that sheer panic gives you. And they took me very seriously.”