The US Coast Guard intercepted a makeshift submarine boat off the coast of Central America — seizing a mountainous $181 million worth of cocaine in what the agency says is its largest drug seizure ever.

California’s Coast Guard Cutter Stratton sailed up to the craft on July 18 after getting a call from a US Navy pilot who spotted the vessel about 200 miles south of Mexico.

The 40-foot-long makeshift boats are a popular form of transportation used by Colombian drug smugglers.

In dramatic video posted online Friday, the Coast Guard members are seen boarding the submarine and immediately placing four smugglers under arrest — after pulling them one by one out of a hatch.

Some of the officers then climb down into the submarine and discover 12,000 pounds of coke in large bales.

The officers then pass the bundles of blow to their counterparts standing on top of the submarine and then the packages are transferred to the Coast Guard boat.

During the process, one of the stunned guardsman on the Coast Guard boat uses his finger to count the growing number of bales piling up on the bow.

Afterward, the boat with the smugglers and narcotics sails back to larger Coast Guard ship.

In the video’s final scene, the camera pans across stacks of cocaine bales on the ship, showing the sheer enormity of the seizure.

Officials say these types of drug busts are becoming common on the high seas.

Just two days before, on July 16, the Coast Guard stopped another submarine-like vessel carrying more than 5,000 pounds of coke.

And over 2,000 vessels packed with narcotics have been intercepted by the Coast Guard since 2006.