Matt. 25:46 - Jesus says, "they will go away into eternal punishment" which is in reference to this eternal fire.
Judith 16:17 - in the day of judgment the Lord will take vengeance on the wicked and they shall weep in pain forever.
The Church is absolutely firm in teaching the reality of hell. The Catechism states: "The teaching of the Church affirms the existence of hell and its eternity. Immediately after death the souls of those who die in a state of mortal sin descend into hell, where they suffer the punishments of hell, ‘eternal fire.’ The chief punishment of hell is eternal separation from God, in whom alone man can possess the life and happiness for which he was created and for which he longs" (CCC 1035).