Railroad official Pham Quynh says passengers were terrified when four cloth bags containing the writhing cobras were spotted Friday. The snakes were alive but had their mouths stitched shut.
Quynh says the exact number of snakes was unclear but the bags weighed 100 pounds.
Security staff removed the cobras, which were likely destined for restaurants in Hanoi. Their owner apparently escaped in the chaos.
Snake meat is considered a delicacy in Vietnam, but cobras are protected by law.
Quynh says the cobras were given to forest rangers who released them into the wild Saturday after no one claimed them.