The World Health Organization warned on Wednesday of a spreading resistance to drugs used to treat the sexually transmitted disease gonorrhoea.
Millions of people with the condition may be at risk of running out of treatment options unless urgent action is taken, the United Nations agency said.
Several countries, including Australia, Britain, France, Japan, Norway, and Sweden have reported cases of resistance to cephalosporin antibiotics -- the last treatment option against gonorrhoea, which affects an estimated 106 million people.
The WHO has called for greater vigilance on the correct use of antibiotics and more research into alternative treatments.
Resistance can be caused by the overuse and poor quality of antibiotics.
"We are very concerned," said Manjula Lusti-Narasimhan, from the WHO's reproductive health unit, "as there are no new therapeutic drugs in development."
"If gonococcal infections become untreatable, the health implications are significant."
Untreated gonorrhoea can cause infertility in both men and women.