The protesters voicing support for Iraqi Shia leader Muqtada al-Sadr, pulled down concrete walls and poured into the Green Zone, the fortified area where many government ministries and the U.S. Embassy are located. Some were also seen walking on tables and waving Iraqi flags.
No lawmakers were present in parliament when the protesters penetrated the Green Zone.
The breach came amid the biggest protest since Iraqi elections were held in October.
In 2016, al-Sadr supporters had stormed the parliament in a similar fashion, staging a sit-in protest and calling for political reform.