A paramedic was verbally abused by a man who then squared up to him while he was treating a collapsed teenager in Harlesden Road.
Police have released a CCTV image of a man they want to speak to over the assault at about 6.20pm on October 9.
The London Ambulance Service was called to the road in Willesden Green after a teenage girl collapsed with breathing difficulties.
When the medic was treating her, a man began shouting abuse at him and then confronted him, putting his finger on his nose.
The medic activated his panic alarm and the man ran off.
The man police want to speak to is in his late 30s, 6ft 2in and was wearing glasses. He had a white jacket on, with a blue shirt, jeans and also had a man bag.
Pc Amanda Scott of Brent Police said: “Such behaviour against emergency service staff, who are only trying to help others, is totally unacceptable.”
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC. Quote CAD 6265/09OCT.
Alternatively, contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here