The huge volcano – technically an eight-mile wide caldera – which is mostly underwater in the Bay of Naples, is bigger than the nearby Mt Vesuvius – which is responsible for one of the deadliest eruptions in human history when it obliterated the nearby Pompeii in 79AD.
The ancient volcano last erupted in 1538 although it was only minor, lasting for eight days.
However, its formation some 39,000 years ago saw lava and rocks thrown hundreds of kilometres away in what was the most violent eruption in the past 200,000 years in Europe.
Robert Isaia, from the Observatory of the National Institute of Geophysics and Vulcanology (INGV), told Welt.de: “The trend is clearly visible.”
Thomas Walter from the German Geo-Research Center in Potsdam added: “The problem is that you can not predict the eruption.”
However, Mr Walter moved to calm any fears by saying: “The signs are already alarming. But there were also strong lifts without breakouts.
Nonetheless, Mr Isaia concludes: “But if the super-bullet breaks out, you should not be there.”
Earlier scientists from University College London and the Vesuvius Observatory warned the volcano “may be approaching a critical stage.”
Christopher Kilburn, Director of the UCL Hazard Centre, said in a paper written for journal Nature Communications: “Further unrest will increase the possibility of an eruption… It’s imperative that the authorities are prepared for this.”
Almost one million people live in Naples with 360,000 living across Campi Flegrei’s caldera.