An eyewitness tells TMZ ... a violent scene unfolded when 2 gunmen on foot and 2 gunmen on Jet Skis approached a man in front of the 5-star Mexican hotel ... and shot him multiple times.

There's currently no word on the victim's identity or why he was shot, but it's suspected this was a cartel hit.

According to local reports, the victim -- a 30-year-old man -- was pronounced dead at the scene. Officers with the Tourist Police Ministry were reportedly the first to arrive, tend to the man and call for paramedics ... but by the time medical assistance arrived, he was dead.

Per reports, one of the gunmen took off following the shooting, running through the beach area near the neighboring Dreams Hotel. The suspect was wearing a black shirt and dark Bermuda shorts.

Video footage from the scene shows first responders covering the body with a blue tarp ... protecting the crime scene for forensic investigators.

This shooting comes more than 2 months after a different bout of violence in Cancun left a 12-year-old boy dead. Gunmen on Jet Skis rained down bullets in the Mexican resort town in an attack against rival drug dealers.

The local boy was sadly a casualty in the incident ... he was declared dead at a nearby hospital after being hit by multiple bullets.