Meaning of màn yán:
màn yán
蔓延
Verb
to spread; to extend
Huǒ shì zài sēn lín zhōng xùn sù màn yán.
火势在森林中迅速蔓延。
The fire spread rapidly in the forest.
Huǒshì yǐjīng kāishǐ mànyán dào fùjìn de sēnlín.
火势已经开始蔓延到附近的森林。
The fire has already started to spread to the nearby forest.