The world is on the cusp of a "post-antibiotic era", scientists have warned after finding bacteria resistant to drugs used when all other treatments have failed.
Their report, published on Wednesday in the Lancet, identifies bacteria able to shrug off colistin in patients and livestock in China.
They said that resistance would spread around the world and raised the spectre of untreatable infections.
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Experts said the worrying development needed to act as a global wake-up call.
Bacteria becoming completely resistant to treatment - also known as the antibiotic apocalypse - could plunge medicine back into the dark ages.
Common infections would kill once again, while surgery and cancer therapies, which are reliant on antibiotics, would be under threat.
Chinese scientists identified a new mutation, dubbed the MCR-1 gene, that prevented colistin from killing bacteria.
It was found in a fifth of animals tested, 15 percent of raw meat samples and in 16 patients.
The resistance had spread between a range of bacterial strains and species, including E coli, Klebsiella pneumoniae and Pseudomonas aeruginosa.
There is also evidence that it has spread to Laos and Malaysia.
Professor Timothy Walsh, who collaborated on the study, from the University of Cardiff, told BBC News: "All the key players are now in place to make the post-antibiotic world a reality.
"If MRC-1 becomes global, which is a case of when not if, and the gene aligns itself with other antibiotic resistance genes, which is inevitable, then we will have very likely reached the start of the post-antibiotic era.
"At that point if a patient is seriously ill, say with E coli, then there is virtually nothing you can do."
Resistance to colistin has emerged before.
However, the crucial difference this time is the mutation has arisen in a way that is very easily shared between bacteria.
"The transfer rate of this resistance gene is ridiculously high, that doesn't look good," said Professor Mark Wilcox, from Leeds Teaching Hospitals NHS Trust.
His hospital is now dealing with multiple cases "where we're struggling to find an antibiotic" every month - an event he describes as being as "rare as hens' teeth" five years ago.
He said there was no single event that would mark the start of the antibiotic apocalypse, but it was clear "we're losing the battle".
The concern is that the new resistance gene will hook up with others plaguing hospitals, leading to bacteria resistant to all treatment - what is known as pan-resistance.
Prof Wilcox said: "Do I fear we'll get to an untreatable organism situation? Ultimately yes.
"Whether that happens this year, or next year, or the year after, it's very hard to say."
Early indications suggest the Chinese government is moving swiftly to address the problem.
Prof Walsh is meeting both the agricultural and health ministries this weekend to discuss whether colistin should be banned for agricultural use.
Professor Laura Piddock, from the campaign group Antibiotic Action, said the same antibiotics "should not be used in veterinary and human medicine".
She told BBC News: "Hopefully the post-antibiotic era is not upon us yet. However, this is a wake-up call to the world."
She argued the dawning of the post-antibiotic era "really depends on the infection, the patient and whether there are alternative treatment options available" as combinations of antibiotics may still be effective.
A commentary in the Lancet concluded the "implications [of this study] are enormous" and unless something significant changes, doctors would "face increasing numbers of patients for whom we will need to say, 'Sorry, there is nothing I can do to cure your infection.'"