The BBC is investigating after several people gained unauthorised access to one of its studios during a live broadcast at Broadcasting House.
A group of five entered the studio at the building in central London at around 19:30 GMT on Friday.
The BBC News channel was using the studio at the time, but the intruders were not seen on air.
It is understood the intruders left of their own accord. A BBC spokeswoman said no one was hurt.
The spokeswoman said: "We take security very seriously and are urgently investigating how several individuals were able to gain access to a studio.
"No one was hurt and there was no interruption to broadcasts.
"We have already taken further security measures and will take any other necessary steps."