Nà dòng lóu shīhuǒ le, xiāofángchē mǎshàng jiù dào.
That building is on fire; the fire truck will arrive soon.
Tips
usage
失火 emphasizes an accidental/uncontrolled fire (失 = to lose control). Compare with 着火, which simply means 'on fire' without implying accident. 纵火 means arson - intentionally set.