Twitter is expanding its use of warning labels, targeting tweets that contain misleading details about coronavirus vaccines.

The decision has been made to strengthen the social network's existing COVID-19 guidance, which has led to the removal of more than 8,400 tweets and challenged 11.5 million accounts worldwide.

Labels providing additional context are already attached to tweets with disputed information about the pandemic.

However, this is the first time the firm has focused on posts about vaccines specifically.

It comes amid ongoing concern about the spread of anti-vaccination material on social media.

In a further effort, Twitter said it is also starting a strike system that "determines when further enforcement action is necessary".

Labels will be enforced by humans only to begin with, which will help automated systems pick up on violating content going forward.

Users will be given a chance on their first strike.

Two strikes will lead to a 12-hour account lock, with a further 12 hours added for a third offence.

A seven-day account lock will be imposed after four strikes, followed by a permanent suspension for five or more strikes.

"We believe the strike system will help to educate the public on our policies and further reduce the spread of potentially harmful and misleading information on Twitter, particularly for repeated moderate and high-severity violations of our rules," the company said.