Likely freebanders (stations operating outside the frequencies they're supposed to be operating on) or fishing fleets using frequencies they're not supposed to. There are often dozens and dozens of these stations active in the 6-7 MHz band alone on a given evening. Most of them seem to come from Latin America and only some of them have been IDed:
They could be fishing fleets, ham operators operating outside the ham bands, unlicensed stations, village radio networks, civil defense systems, radiotelephone networks for remote locations, drug traffickers using HF radio, or some combination of the above. They are collectively known as "peskies" (from the Spanish term "pescadores" - which means "fishermen")
Check out the Peskies subforum for logging similar transmissions:
https://www.hfunderground.com/board/index.php/board,34.0.html