The Metropolitan Police, however, clarified the incident that took place yesterday was not related to terrorism.
The woman, believed to be in her 30s, was quickly detained by officers before she gained access to the palace grounds.
She was arrested on suspicion of trespass under Section 128 of the Serious Organised Crime and Police Act 2005, trespass on a designated site and is currently in custody at a central London police station, the Met Police said.
A crowd of tourists had gathered, with many of them filming the incident on their phones.
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The railings on the side of Queen Elizabeth IIs official London home are 21-feet-high compared to the gates which stretch to 29-feet.
There have been a number of other incidents in recent years in which people have tried to get into the palace grounds. Last year, a 21-year-old man was arrested for climbing over a side wall to the palace.