The underwater explosion took place Friday, which was actually noticeable from satellites all the way up in space ... and the images captured of the moment the volcano blew are mind-blowing, giving you a true sense of how powerful this thing was -- and how devastating too.

The real-world effects were felt almost immediately ... not only did people hear and see the mighty boom, but soon -- there were massive waves crashing ashore on the island of Tongatapu. Several videos were posted of the early damage, and even then ... it was bad.

Check out some of these clips ... you can see water tearing through residential areas and ripping down gates and fences. Some areas seem to have been hit harder than others.

There's one video that looks like it's straight out of a movie (in a bad way), with massive waves bursting their way onto the city streets ... and cars having to do quick U-turns to get the hell out of there.

So far, there are no reports of injuries or deaths -- but at the same time, much of the island is without communication or internet at the moment ... that's how rocked they've been over the past 10 hours or so.

Now, the rest of the world (at least on the Pacific side) is starting to feel the ramifications from this ... including here in the States, where weather officials have issued tsunami warnings in Hawaii, Alaska, British Columbia and all up and down the west coast of the U.S.

There are reports of massive waves crashing against the shorelines in cities like Monterey and elsewhere ... and locals have been told to steer clear of the area for a while.