Boris Johnson showed New York's Mayor how he keeps London's streets safe today - but found himself caught up in a security tangle.
One security guard was bundled off his feet as officers grappled with photographers and cameramen as they filmed Mr Johnson giving Michael Bloomberg a tour of the CCTV network at Westminster Tube.
Mr Bloomberg praised London's record in "standing up to terrorism" during the visit in the wake of the failed Times Square bomb plot in the US city.
But witnesses told how a row erupted with security officers and members of the media as the two mayors were ushered into a small room.
The onlooker, who did not want to be named, said: "There were extra security officers for Mr Bloomberg and there was also more media than had been expected.
"As a result there was a lot of pushing and shoving. It was chaotic."
A spokeswoman for Mr Johnson played down the incident.
She said: "I think it was all contained. It was just a bit of a media scrum."
No arrests were made.
During the visit, Mr Johnson explained to Mr Bloomberg how the capital uses CCTV to fight terror.
London has 12,000 cameras on the Tube network, which will rise to more than 14,000 over the next few years, a spokeswoman said.
Mr Johnson said: "We are never complacent, and there always painful reminders that we must never let down our guard, but it is clear that the approach we are taking - with sustained investment in policing and CCTV - is helping us make significant strides along the road of tackling crime in our city."
Mr Bloomberg said: "London has a history of standing up to terrorism - and I am here to learn from others, see what works best, and try to fix things before they become a problem.
"We will continue to work closely with London to do whatever we can to keep our cities safe."