The deaths of hundreds of wild birds along Mexico's Pacific coast were likely caused by the El Niño climate phenomenon, local authorities said on Thursday, as the country and its surrounding oceans face an intense heat wave, Reuters reported.

Some 300 wild birds of various species were found dead over the weekend along the coasts of Mexico's western states of Chiapas, Oaxaca, Guerrero, Michoacan, Jalisco, Sonora and Baja California Sur.

Authorities had initially suspected avian influenza, but a joint effort from the country's agriculture and environment ministries concluded the most likely reason was warmer oceans resulting from El Niño.

The periodic natural phenomenon, which lasts between months and years, warms the Pacific Ocean fuelling tropical cyclones, floods and rainfall across the Americas and elsewhere.

The US National Oceanic and Atmospheric Administration (NOAA) earlier this month declared that an El Nino is now under way, after three years dominated by the cooler La Nina pattern.

Scientists say this year looks particularly worrying, as coupled with climate change, the current phase should see the world grapple with record-high temperatures.

With warmer waters, fish tend to swim lower in search of colder waters, which prevents seabirds from successfully hunting for their food, the ministries said in a statement.

Sea birds were also found dead on the coasts of Peru and Chile, Mexican authorities said.

At least six people have died in Mexico as a result of intense heat this warmer season, according to recent tally from the health ministry. The country is facing a heat wave with temperatures surpassing 43 Celsius (109.4 Fahrenheit) in parts of the country.