US forecasters say potentially record-breaking El Niño underway

The presence of an El Niño will likely bring less rainfall and warmer temperatures to parts of Australia. (Supplied: Taryn Seccombe)

The US National Oceanic and Atmospheric Administration says an El Niño is now underway in the Pacific Ocean.

In Australia, the presence of an El Niño can intensify drought, bushfires and heatwaves.

There is a 63 per cent chance this year's El Niño could be one of the largest events since records began in 1950.

The US meteorological agency has declared an El Niño has now formed in the Pacific Ocean and warned it could reach record-breaking intensity in coming months.

The National Oceanic and Atmospheric Administration (NOAA) officially confirmed the existence of the El Niño, which is a warming of the Pacific near the equator that affects weather patterns across the globe.

NOAA's announcement said there's a 63 per cent chance that the El Niño will get so intense over the Southern Hemisphere's spring and early summer that it "would rank among the largest El Niño events in the historical record going back to 1950."

Experts said the El Niño, a natural warming cycle, should further heat a globe already warming from fossil fuel pollution and will likely turbocharge extreme weather across the planet.

It was Peruvian fishermen, hundreds of years ago, who first noticed and named El Niño. Little did they realise they had named one of the most consequential climate drivers on Earth. This is how it works.

Meteorologists forecast it will rival — or exceed — a record El Niño that began in 1997 and helped trigger billions of dollars in damage from heat waves, floods, droughts, tornadoes and wildfires.

Clark University climate scientist Abby Frazier said the warm, deep waters of an El Niño affect weather patterns by bringing "a lot of extra heat to the surface, fueling a lot of extreme events for a lot of places around the world".

She said, especially in the Pacific, that "it can get dire very quickly".

United Nations Secretary-General António Guterres described El Niño as an "urgent climate warning."

"El Niño conditions will pour fuel on the fire of a warming world," Mr Guterres said in a video message.

Forecasters use a region of the Pacific Ocean to determine whether an El Niño or La Niña is underway. (Supplied: NOAA)

The weather pattern's effects vary by region. El Niño often dampens — but does not eliminate — Atlantic hurricane season activity, but increases the chance of cyclones and typhoons in the Pacific.

In Australia, the climate driver can intensify drought, bushfires and heatwaves.

So while the US East and Gulf