Keep your toilet lid closed when you flush - that's the advice being pushed by researchers in their continuing fight against the Covid-19 pandemic.

A Chinese study has revealed what goes down when you flush a toilet, and importantly, what stays up.

Published in the journal Physics of Fluids, the research showed that when a toilet is flushed, a cloud of tiny droplets is propelled up to three feet in the air.

These micro-particles can then 'hang' in the air for up to one minute - enough time to be breathed in by the next person needing to go.

Recent studies show the Covid-19 virus can survive as it passes through a person's digestive tract, becoming present in their feces.

A flushing toilet is known to disperse other virus and bacteria in the air, in a process known as fecal-oral transmission.

Though person to person transmission of Covid-19 via this way wasn't clearly established by the study, the researchers say it's entirely possible, given the evidence.The team from Yangzhou University analysed computer models that simulated the water and airflow in two types of flushing toilets.

They discovered that when water hits the toilet bowl, a large amount of turbulence is generated, leading to the formation of vortices. These vortices continue upwards past the bowl and into the air, accelerating droplets of fecal matter to speeds of up to five metres per second.

''The simulation results are alarming in that a massive upward transport of virus particles is observed,'' reports the study. ''In addition, 40%–60% of particles reached above the toilet seat, leading to large-scale virus spread.''

The investigators recommended that people close toilet lids when they flush and practice good hygiene, such as thoroughly washing their hands and cleaning the toilet seat before use.

With lockdown measures easing in some countries, people are now returning to the office and other public spaces such as shops and parks.

However, public and work toilets could still pose a risk for spreading Covid-19, particularly in facilities with no toilet lid to put down.

The study authors note: ''Blocking the path of fecal-oral transmission, which occurs commonly in toilet usage, is of fundamental importance in suppressing the spread of viruses. However, to date, efforts at improving sanitary safety in toilet use have been insufficient.''

The study authors also recommend manufacturers start rethinking toilet designs to help minimize the spread of other viruses and bacteria when they flush