Witnesses have described an "almighty smash" and officers with Tasers and "rifles" shouting at a person after a automotive drove into the Downing Street gates.
One individual was arrested after a hatchback hit the metal barrier at round 4.20pm.
Video confirmed it crossing Whitehall, apparently from the course of a Ministry of Defence automotive park reverse, however then showing to decelerate because it approached.
Police mentioned a person had been detained on suspicion of prison harm and harmful driving.
No one was harm.
Witness Simon Parry, 44, mentioned: "I heard a bang and looked up and saw loads of police with Taser guns shouting at the man.
"A variety of police autos got here in a short time and had been very fast to evacuate the realm."
He said the man had his "face to the ground" and that "there have been sniffer canines and a bomb squad".
Mr Parry added: "We noticed those who had been in a panic working away and we noticed individuals who had been excited."
Another witness, Krish Kandiah, who was coming into Downing Street on the time, mentioned he heard an "almighty smash at the front gate, which was metres away from us".
"Immediately we saw police scramble and armed officers responded swiftly and shouted at the man to get out the car," he mentioned.
Mr Kandiah - who was handing in a petition - estimated there have been 10 armed officers with "rifles" across the man.
"He was wrestled out of the car very quickly and put down on the ground and handcuffed and his vehicle was then searched," he mentioned.
He praised police, who pushed his group by safety and fashioned a "human shield" to guard them.
The highway outdoors Downing Street was cordoned off after the incident as police searched the automotive - which had its boot open.
Sky News correspondent Joe Pike, on the scene, mentioned officers appeared calm and "not on edge at all".
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