Armed police have arrested two women at Liverpool Street station and the area was evacuated.
Police searched the station after the arrests were carried out
Plain clothes officers "burst into" the station, pinning the women down and causing "chaos", an eyewitness said.
Scotland Yard officers arrested the pair around 1354 BST before both the mainline and Underground stations were evacuated, along with nearby streets.
British Transport Police said: "A number of packages were examined, but the stations have now been reopened."
The incident came as two more of the failed London bombing suspects were thought to have been arrested amid a number of armed operations in London.
One of the women is understood to have been in a queue for the Stansted Express when she was pushed to the ground by police.
An eyewitness told BBC News that plainclothes police "suddenly burst into the main centre of the station and arrested two women".
"Initially there was obviously a bit of chaos. They tried to push people away and tried to stop people taking pictures with their mobile telephones," he said.
"They were gradually pushing people further and further back."
The eyewitness went on: "They pinned them down on the floor, put their hands behind their backs, put handcuffs on them and took them away."
After describing the evacuation of the station and nearby streets, the eyewitness added: "There are now hundreds of people surrounding the station who were trying to catch a train and can't get in."
Gates to the Underground station were opened at 1520 BST.
Three police vans and a police car remained parked outside Liverpool Street after the reopening.
Dozens of officers stood guard in the station and helped commuters with their journeys.
Passengers on both Underground and mainline services have been able to board their trains.