Jane Manchun Wong found the code, which has not been activated.

Instagram, which is also owned by Facebook, is conducting a similar test in seven countries including Canada and Brazil, where only the account holder in the trial can see the number of likes they attract.

Facebook declined to comment.

Some studies have suggested the pressures of social media popularity can affect mental health, particularly in young people.

• Are we addicted to the ‘like’ button?

Ms Wong wrote a blog post about her discovery, in which she emphasised that she does not work for the tech giant.

"It takes time to develop, observe, research and release experimental features like this," she said.

"Experimental features could come and go. But I am certain hiding the public like counts will be beneficial to the digital wellbeing of a large chunk of users."

Venture capitalist Ellen Pao tweeted that the change - if it happens - is overdue.

"Social platforms have known as early as 2014 that social media impacts mental health and only now is Facebook starting to hide like counts," she said.

Instagram said it was not yet ready to share the results of its experiment.

"We hope this test will remove the pressure of how many likes a post will receive, so you can focus on sharing the things you love," Mia Garlick, Facebook Australia and New Zealand director of policy, said in a statement when the Instagram trial was announced.