Hurricane Melissa made landfall in Jamaica a couple of hours ago ... and the Category 5 storm was immediately wreaking havoc on the island.

The massive storm is causing roads to flood -- in some areas, flash flooding pushed water high enough to engulf a car -- and major power outages across the country are occurring ... with CNN reporting nearly 250,000 are impacted.

In harrowing videos shared by local radio news station Nationwide90FM ... Melissa's winds were so furious, reaching 185 MPH ... they ripped a portion of the roof off Savanna La Mar Hospital. Another hospital was also damaged, per the station.

Just before Melissa made landfall ... the National Hurricane Center issued a stark warning to Jamaicans ... "To protect yourself from wind, the best thing you can do is put as many walls as possible between you and the outside. An interior room without windows, ideally one where you can also avoid falling trees, is the safest place you can be in a building. You can cover yourself with a mattress and wear a helmet for added protection."