Twitter is to delete "unverified claims" that could lead directly to the destruction of critical infrastructure or cause widespread panic.
It changed its rules following a series of attacks on mobile phone towers in the UK, fuelled by the spread of false conspiracy theories on social media.
Twitter said it would not remove 5G and coronavirus misinformation, but would remove direct incitement to action.
Tweets that could cause "widespread panic" will also be removed.
Twitter gave two examples of tweets that would violate its new policy:
- "5G causes coronavirus! Go destroy the cell towers in your neighbourhood!"
- "The National Guard just announced that no more shipments of food will be arriving for two months! Run to the grocery store and buy everything."
Scientists say the idea of a connection between Covid-19 and 5G is "complete rubbish" and biologically impossible.
The conspiracy theories have been branded "the worst kind of fake news" by NHS England medical director Stephen Powis.
On 20 April, media regulator Ofcom found TV channel London Live to be in breach of standards for an interview it aired with David Icke on coronavirus.
It said Icke had "expressed views which had the potential to cause significant harm to viewers in London during the pandemic".