Her mother said she had been "counting down the days" to see her daughter again, who had been au pairing in Herne Hill.

Her daughter had been out celebrating a new job in Westminster.

"Absolute terror - we were counting down the days to see her, I haven't seen her for three months, she went in March on this wonderful trip away, life experience," her mother said.

"Saying that, I was encouraging her to do it because life experience at 21 is so good.

"But horror, absolute horror."

In a Facebook post titled “Missing from London Terror Attack”, a family friend, who has been working as a nanny, called out for people to share information about her possible whereabouts.

“Dear friends please can I ask you to share this post. My friend’s daughter, Sara Zelenak, was last seen on London Bridge and was witness to the terror attacks,” says the message, which has since been removed.

“She got separated from her friends and has not been seen since. Her phone has rang with no reply and now the battery must have gone… She calls her mum daily. It’s been over 24 hours with no news from the consulate.”

Her mother told a local news site: "The last time I spoke to her was our time Friday afternoon at 4:42 and she said, 'Oh mum! It's only 28 days until you and I and dad can have baguettes and cheese and croissants in Paris.