The number of measles cases reported worldwide in the first three months of 2019 has tripled compared with the same time last year, according to the World Health Organisation (WHO).
The UN body said provisional data show just over 112,000 cases in January, February, and March. They said it indicated a "a clear trend", with all regions of the world seeing outbreaks, with African countries facing the most dramatic rise - up 700 percent.
The agency said actual numbers may be far greater, since only one in 10 cases globally are reported.
Measles is a highly infectious viral illness that can lead to serious health complications - including infections of the lungs and brain - and even death.
Ukraine, Madagascar and India have been worst affected by the disease, with tens of thousands of reported cases per million people.
Since September, at least 800 people have died from measles in Madagascar alone.
Outbreaks have also hit Brazil, Pakistan and Yemen, "causing many deaths - mostly among young children".
A spike in case numbers was also reported for the US and Thailand with relatively high levels of vaccination coverage.
The UN said the disease was "entirely preventable" with the right vaccines, but global coverage of the first immunisation stage had "stalled" at 85 percent, "still short of the 95% needed to prevent outbreaks".
In an opinion piece for CNN, WHO heads Henrietta Fore and Tedros Adhanom Ghebreyesus said "the proliferation of confusing and contradictory information" about vaccines was partly to blame.
"It is understandable, in such a climate, how loving parents can feel lost," they said, but added that "ultimately, there is no 'debate' to be had about the profound benefits of vaccines".
"More than 20 million lives have been saved through measles vaccination since the year 2000 alone."
In response to recent measles outbreaks, calls have mounted in several countries to make immunisation mandatory.
Last month, Italy banned children under six from attending schools unless they had received vaccines for chickenpox, measles and other illnesses.
A public health emergency has also been declared in areas of New York, ordering all residents to be vaccinated or face a fine.