The blood of San Gennaro, or Saint Januarius, failed to liquefy on Wednesday despite a long day of prayer, reports Italian bishops' newspaper Avvenire.
A vial containing what is said to be the dried blood of the patron saint of Naples is put on display three times a year in the city’s cathedral, as people gather to pray and witness it liquifying.
The event is known as the “Miracle of San Gennaro”.
But it didn't happen on Wednesday despite hours of praying in the morning and a special mass in the afternoon.
This time, fewer people than normal were allowed into the cathedral because of coronavirus restrictions.
Many people in Naples, and the superstituous south of Italy in general, take the 'miracle' as a reassuring sign.
But people get particularly nervous if the blood does not liquefy on the saint’s feast day, September 19th. While still thought to be a bad sign, it is seen as less serious on the other two occasions – December 16th, and the Saturday before the first Sunday in May.
On some (but not all) previous occasions when the blood has failed to liquefy, bad news soon followed for Naples, and the rest of Italy.
In September 1980, the miracle failed to occur and two months later the area around Irpinia, east of Naples, suffered a devastating earthquake that killed almost 3,000 people.
The miracle also failed to happen in 1939 and 1940 – coinciding with the beginning of world war two and Italy's entry into the conflict, and again in September 1943: the date of the Nazi occupation of Italy.
The city’s cardinal, Crescenzio Sepe, tried to reassure people on Wednesday that there was “no omen of disasters, nor epidemics, nor wars: we are men and women of faith.”
He added: “If something needs to melt, it is the hearts of people.”
The Catholic Church supports the events, but has never issued a formal statement on the 'miracle'. However it has forbidden anyone, including scientists, from opening the sealed vial.
Scientists, who say the substance in the sealed vial does appear to be dried blood, can't explain why it sometimes turns into liquid and sometimes does not.