Cold Case Christianity has a post detailing the statements on hell by a number of ante-Nicene fathers--it is a valuable resource in considering this questions; I discovered several of the quotations below from their research.
Perhaps the most graphic of these statements is that by Lactantius in the early 4th century:
For because they have committed sins in their bodies, they will again
be clothed with flesh, that they may make atonement in their bodies;
and yet it will not be that flesh with which God clothed man, like
this our earthly body, but indestructible, and abiding forever, that
it may be able to hold out against tortures and everlasting fire…The
same divine fire, therefore, with one and the same force and power,
will both burn the wicked and will form them again, and will replace
as much as it shall consume of their bodies, and will supply itself
with eternal nourishment (Divine Institutes 7:21)
In fairness, this is a statement made hundreds of years after the apostles. Some earlier sources are worth citing as well:
Ignatius of Antioch (a disciple of John, writing early 2nd century)
Corrupters of families will not inherit the kingdom of God. And if
they who do these things according to the flesh suffer death. how much
more if a man corrupt by evil reaching the faith of God. for the sake
of which Jesus Christ was crucified? A man become so foul will depart
into unquenchable fire: and so will anyone who listens to him. (Letter
to the Ephesians 16:1-2)
Irenaeus of Lyons (writing late 2nd century)
the Saviour of those who are saved, and the Judge of those who are
judged, and sending into eternal fire those who transform the truth (Against heresies 3.4.2)
Irenaeus didn't really mince words. Relevant to the discussion of Irenaeus, you may find this article by Brad Kelly interesting: Did the early church believe in a literal hell of eternal punishment
The earliest clear source for annihilationism (essentially that the wicked are annihilated rather than existing eternally) would be Arnobius of Sicca in the 4th century; the idea is discussed in detail by Talbot here. Talbot points out that Arnobius' ideas were repeatedly opposed by his contemporaries and later generations.
In general, it appears to me that the writings grew more extreme (and grotesque!) over time, but that in the earliest sources we find comments pretty similar to those in the New Testament. By the 4th century we see departure at both extremes (annihilation and...regeneration??).
But the early sources don't seem to be focused so much on the nature of the fire. They could be read to indicate either literal fire or as a metaphor of agony.
J. Warner Wallace summed it up as follows:
The Early Church Fathers, with very few exceptions, agree with
traditional views descriptions of Hell as a place of eternal,
- Hell is a place of judgment for those who have rejected God and denied Jesus as their Savior
- Hell is a place of separation from God
- Hell is a place of torment in which the rebellious are in anguish and pain
- Hell is a place where the rebellious are tormented forever and are conscious of this torment for all eternity (In fact, the eternal
duration of their torment is often compared to the eternal duration of
the reward of the saved)
At the same time, the earliest Church Fathers are ambiguous on those
areas where the Bible is ALSO ambiguous.
- The exact nature of the torment of the rebellious is unknown
- The manner in which the rebellious are kept alive in spite of ‘deathly’ anguish is also un-described