Facebook Inc's photo-sharing social network Instagram said on Thursday it has fixed a bug that led to a temporary change in the appearance of its feed for a large number of users.

The bug led to a small test being distributed widely, the company said. As part of the test, some users had to tap and swipe their feed horizontally to view new posts, similar to its Stories feature.

The momentary change sparked a widespread outrage among users on Twitter, with several comparing it to Snapchat's unpopular redesign.

"The Instagram update is so trash it's worse than the Snapchat update," @samfloresxo tweeted.

The redesigned Snapchat app has struggled to attract more users since its roll-out last year and newer versions have been criticised for being too confusing.

In response to a tweet, Head of Instagram Adam Mosseri apologised for the confusion and said, "that was supposed to be a very small test that went broad by accident."

"We quickly fixed the issue and feed is back to normal," Instagram said in an emailed statement.