The WMO statement follows several scorching days which saw global temperature records soar.
The first week of July was the hottest week on record, according to data from the UN's World Meteorological Organization (WMO). Last Thursday saw the daily global average peak at 17.08 Celsius.
"The world just had the hottest week on record, according to preliminary data," the WMO said in a statement.
Last month, climate change and the early stages of the El Niño weather pattern drove the hottest June on record.
The news comes as a study published in the science journal Nature reveals Europe saw more than 61,000 heat-related deaths last summer. Italy, Greece, Spain and Portugal were the countries worst affected.
What's behind this summer's heatwave?
El Niño is a natural climate phenomenon associated with warmer ocean surface temperatures in the central and eastern tropical Pacific Ocean. The current episode is likely to continue with "at least moderate intensity", according to the WMO.
The announcement follows a series of scorching days which saw global temperature records soar.
Cities in France recorded maximum temperatures of 37°C-38°C on Sunday. The country's national forecaster Météo-France said this was a non-exceptional heatwave episode for the season, but it required vigilance due to its persistence.
Preliminary data from the German Weather Service (DWD) showed temperatures also reached 38°C in Tönisvorst in North Rhine-Westphalia on Sunday.
This series of unprecedented temperatures began on 3 July (16.88°C), beating the previous record of 16.80°C set in August 2016, the hottest year ever measured by Copernicus.
Over 60,000 heat-related deaths
Scientists say crushing temperatures that blanketed Europe last summer may have led to more than 61,000 heat-related deaths, highlighting the need for governments to address the health impacts of global warming.
The increase in heat-related deaths was higher among older people, women, and in Mediterranean countries, according to the study by the Barcelona Institute for Global Health. But the data also indicated that measures taken in France since a deadly heatwave two decades ago may have helped prevent deaths there last year.
France’s warning system includes public announcements with advice on how to stay cool and encouraging people to drink water and avoid alcohol.