Talk about a nightmare neighbor … residents of an apartment building in China got the scare of a lifetime when a massive, nearly 18-pound king cobra came slithering right past their windows … and it’s all on video.

The terrifying encounter went down Sunday afternoon in Liupanshui, a city in southwestern China … where the enormous snake was caught on video crawling along the metal railings outside the building.

The venomous reptile was seen making its way along the exterior of the building, getting dangerously close to people’s windows — that’s one visitor you definitely don’t want dropping by unannounced.

One resident, identified as Mr. Zhu, told local media he’d never seen a snake so big … and suspected the creepy crawler came from a nearby hillside.

Firefighters were called to the scene and managed to capture the cobra … which tipped the scales at a whopping 17.6 pounds.

And this wasn’t just any snake … king cobras are the world’s largest venomous snake species, with bites that can be deadly.

Snake experts warn the reptiles generally won’t attack unless they feel threatened … but recommend keeping a VERY safe distance if you ever encounter one.