Image copyright AFP/Getty Image caption Perry is top of the Twitter charts

The US singer-songwriter Katy Perry has become the first person to reach 100m followers on Twitter.

The website posted a video compilation of her tweets since she joined in 2009 along with a message saying "Today, we #WITNESS history".

Witness is the name of Perry's new album.

The Canadian singer Justin Bieber has the second highest number of followers at 96.7m with Barack Obama in third place with almost 91m.

The rest of the top 100 accounts are mostly made up of singers, sports stars, media companies and a few politicians, according to the website Twitter Counter.

US president Donald Trump is the most-followed current leader, in 33rd place with 32.4m followers. Two places behind him - after the boy band One Direction - is Indian Prime Minister Narendra Modi with 30.7m followers.

Image copyright Twitter/Katyperry Image caption The singer thanked Twitter after hitting the milestone

However it is not clear how many of these accounts' followers are real people and how many may be fake accounts.

Searches using the tool Twitter Audit - which analyses a sample of followers and calculates a score based on factors including the number of tweets they have sent - suggested that about two-thirds of both Perry's and Bieber's followers may not be real.

For Mr Obama and Mr Trump the figure dropped to about a third.

In January researchers in the UK discovered massive collections of dormant fake Twitter accounts.

Some had been used to fake follower numbers, send spam and boost interest in trending topics, the researchers found.

Twitter says users are banned from writing programs that automatically followed or unfollowed accounts or which "favourited" tweets in bulk.

Image copyright AFP/Getty Images Image caption Katy Perry has become known for her bold fashion choices over the years

Top five most-followed Twitter accounts

Four are pop stars, one is a former US president.

@katyperry 100m followers

@justinbieber 96.7m followers

@BarackObama 90.8m followers

@taylorswift13 85.1m followers

@rihanna 74.1m followers