Japan has seen its hottest September since records began 125 years ago, the weather agency said, in a year expected to be the warmest in human history.

The scorching September's average temperature was 2.66 degrees Celsius higher than usual, the Japan Meteorological Agency said on Monday.

This was "the highest figure since the start of statistics in 1898", the agency said in a statement.

This year is expected to be the hottest in human history as climate change accelerates, with countries including Austria, France, Germany, Poland and Switzerland each announcing their warmest September on record.

Across Japan last month, 101 of 153 observation locations broke an average temperature record, including in Tokyo, with an all-time high of 26.7 degrees Celsius (80 degrees Fahrenheit), in Osaka with 27.9C and in Nagoya with 27.3C.

The average temperature jump of 2.66C was "extraordinary" and "easily topped previous highs", weather agency official Masayuki Hirai told AFP on Tuesday.

"If this is not an abnormally high temperature, I don't know what is," he said.

French weather authority Meteo-France said the September temperature average in the country will be around 21.5 degrees Celsius, between 3.5C and 3.6C above the 1991-2020 reference period.

The UK, too, has matched its record for the warmest September since its records began in 1884.

The average global temperature in June, July and August was 16.77 degrees Celsius, surpassing the previous 2019 record, the European Union's Copernicus Climate Change Service (C3S) said in a report.

In September, UN Secretary-General Antonio Guterres told world leaders the climate crisis had "opened the gates to hell".

In his opening address at the Climate Ambition Summit, Guterres evoked this year's "horrendous heat" but stressed: "We can still limit the rise in global temperature to 1.5 degrees," referring to the target seen as needed to avoid long-term climate catastrophe.