sea of fire; blazing inferno
Idiomatic expression describing a large area engulfed in flames, often used in dramatic or literary contexts.
爆発の後、工場は火の海と化した。
After the explosion, the factory turned into a sea of fire.
The forest became a blazing inferno due to the wildfire.
Compound of 火 (hi, 'fire') + の (no, possessive particle) + 海 (umi, 'sea'), literally 'sea of fire'. The expression is straightforward and its origin is transparent.