The highly-contagious disease can be entirely prevented through a two-dose vaccine, but experts have in recent months sounded the alarm over declining vaccination rates.
According to new data by the United Nations health agency, 364,808 measles cases have so far been reported globally in 2019, up from 129,239 cases last year.
The number is "the highest [registered] since 2006," WHO spokesman Christian Lindmeier told reporters in Geneva on Tuesday.
The rapidly-growing figure is especially worrying since only about one in 10 actual measles cases is believed to be reported worldwide, according to the WHO.
Measles cases have soared around the world, with the African region seeing a 900-percent jump in cases year-on-year, while cases rose 230 percent in the western Pacific.
The Democratic Republic of the Congo (DRC), Madagascar and Ukraine registered the highest number of cases, while Angola, Cameroon, Chad, Kazakhstan, Nigeria, the Philippines, Sudan, South Sudan and Thailand have all seen major outbreaks of the disease.
The United States has registered 1,164 cases so far this year, compared with 372 for all of 2018 and the highest number on record in a quarter-century.
And in the European region, nearly 90,000 cases have been registered this year - well above the 84,462 cases recorded last year.
Meanwhile, in Madagascar, which registered around 127,500 cases during the first half of this year alone, numbers have dropped considerably in recent months following an emergency national vaccination campaign, the WHO said.