Police believe a suspicious fire that destroyed a gym in Melbourne's south-east was targeted.

Arson and Explosive Squad, Echo Taskforce and VIPER are investigating whether the incident was linked to a series of arson attacks attributed to organised crime groups and outlaw motorcycle gangs.

Firefighters were called to Fighters Xpress gym in Dandenong after receiving multiple calls reporting a structure fire 3.45am.

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The gym was fully involved in flames when crews arrived on the scene, a Fire Rescue Victoria spokesperson said.

A cafe next door was also engulfed.

Fire crews extinguished the blaze and the incident was handed over to Victoria Police.

Detective Inspected Chris Murray said it was a scene of "absolute devastation".

A Victoria Police spokesperson said a car was used to crash through the front door of the gym shortly after 3.30am.

"The offenders have poured accelerant through the building before setting it on fire and fleeing," the spokesperson said.

"A short time later, emergency services were notified of a vehicle fire on Canberra Avenue in Dandenong which is believed linked."

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FRV Paul Foster said the building was "quite severely damaged".

"The structural integrity has been compromised. We managed to cut the fire off before it reached other adjoining buildings," he said.

The fire has been deemed suspicious.

"We will be significantly upping the ante as a result of this," Murray said.

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A fire that broke out inside a high-rise unit complex on the Gold Coast last night has been deemed non-suspicious.

Police responded to the fire on the 10th floor about 12.45am at the Equinox Sun Resort in Surfers Paradise.

About 82 people were treated at the scene by paramedics, some for smoke inhalation, with video showing one resident climbing across the building to escape.

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"Flames were blowing into his face and he obviously had nowhere to go," one witness told 9News.

"He was an older guy. I was more concerned because he was trying to climb the balcony to get into next door."

Four people were taken to hospital, including a man in his 40s with non-life-threatening injuries.

All patients are in a stable condition. 

Residents have been allowed back into the building.

The police investigation has now finished, with officers saying the fire was not suspicious.

Queensland Fire and Emergency Services is continuing to investigate the cause.

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Italian authorities have issued an "extreme" health risk for 16 cities including Rome and Florence this weekend as a heat wave that is baking Europe threatens to bring record temperatures.

Climate scientists at the European Space Agency (ESA) say temperatures could reach 48 on the islands of Sicily and Sardinia, "potentially the hottest temperatures ever recorded in Europe."

Rome could get as hot as 44.

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Italian authorities have issued the second-highest heat warning to nine other cities.

The country's health ministry is advising the public to stay hydrated, eat lighter meals and avoid direct sunlight between 11am and 6pm.

The ESA warned that Europe's heat wave has only just begun with Spain, France, Germany and Poland expected to see extreme weather, just as the continent welcomes what is expected to be a record-breaking number of tourists coming for the first time since the COVID-19 pandemic.

Greece shut the Acropolis of Athens for a second straight day on Saturday amid fierce temperatures. Local police helped a tourist who got into difficulty on Friday.

There is particular concern over those working outdoors after a 44-year-old construction worker in Italy died after collapsing on a roadside earlier in the week.

Authorities in Spain warned the heat wave is not just hitting the usual frying pan areas in the south, but also affecting the country's typically cooler north.

In the south, temperatures in the cities of Seville, Cordoba and Granada have reached 40.

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Spain's national weather service says it's also sizzling on Spain's resort island of Mallorca in the Mediterranean Sea with highs of 36 degrees Celsius.

Meanwhile, even the normally mild region of Navarra in the north is seeing up to 40 degrees Celsius.

A wildfire that broke out on La Palma Island in Spain's Canary Islands burned several homes and forced the evacuation of 500 people, the Canary Islands regional government tweeted on Saturday morning.

Heat is one of the deadliest natural hazards – more than 61,000 people died in Europe's searing summer heat wave last year.

The current heat wave – named "Cerberus" by the Italian Meteorological Society after the three-headed monster that features in Dante's "Inferno" – has prompted further fears for people's health, especially as it coincides with one of the busiest periods of Europe's summer tourist season.

Europe is not the only place facing extreme temperatures.

A dangerous weeks long heat wave in parts of the western United States is set to worsen this weekend, with more than 90 million people under heat alerts.

Temperatures in some desert areas were predicted to soar past 48.8 during the day, and remain above 32.2 overnight.

Around 200 hydration stations distributing bottles of water and cooling centers where potentially thousands of people can rest in air-conditioned spaces opened on Saturday in public spaces like libraries, churches and businesses around the Phoenix area.

By mid Saturday afternoon, it was 50 in Death Valley, California, where forecasters have said the temperature could hit 54.4 this weekend.

The hottest temperature recorded at Death Valley was 56.6 C in July 1913, according to the National Park Service.

The extreme weather is even taking affects as far afield as Australia, with Sydney experiencing unseasonably warm weather for its winter months, according to the country's Bureau of Meteorology.

It was 23 on Saturday, around 6 more than average.

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