Archbishop of Naples, Crescenzio Sepe, announced that the blood had changed state on Wednesday at 5.50pm - a little later than in previous years.
Each year thousands of Roman Catholic faithful flock to three special services at Naples Cathedral where the dried blood of the fourth-century martyr is said to turn to liquid.
The showing of the vial is eagerly awaited because, according to tradition, whenever the blood has failed to liquify a catastrophe has occurred. The vial is also shown on January 19th, the Saint's feast day, and on the Saturday before the first Sunday of May.
The December ceremony, which has been going on for the past four centuries, remembers the end of a volcanic eruption which devastated much of the countryside around in Naples in 1631, but stopped short of the city: a slice of good fortune credited to the intervention of Januarius.
In 1527 and 1528 non-liquefaction was followed by the plague. In 1559 famine came and in 1833 cholera raged through the city. In 1944 during World War II non-liquefaction was proceeded by bombing raids by Allied aircraft.
While no statement has ever been issued by the Catholic church on the phenomenon, a number of scientific theories have been put forward to explain the blood miracle.
Many have argued that given the prominence of similar blood rites across the surrounding Campania region, the 16th century artisans and alchemists of Naples must have had a "recipe" for saints' blood that allowed them to produce so many of these relics.
The blood half-liquefied in March during a ceremony when Pope Francis held and kissed the relic while on a visit to Naples.
Saint Januarius was was decapitated during the persecution of Christians during the reign of the emperor Diocletian in 305 AD.