Passengers travelling on public transport in London are being told to wear face coverings.
Transport for London (TfL) said the measure could prevent people with coronavirus infecting others.
Face coverings can commonly mean a scarf, piece of cloth or mask.
They could help prevent you from giving it to othersTfL
The announcement covers passengers using the London Underground network, buses, black cabs and minicabs.
Some transport users were already covering their faces, but it was not mandatory.
TfL said in a statement: “Please travel outside of peak times and use a facial covering, carry a hand sanitiser and wash your hands before and after you travel.
“The latest Government advice is that, although face coverings are unlikely to prevent you from getting the virus, they could help prevent you from giving it to others.
“Face coverings are particularly important where two-metre social distancing is hard to maintain.”