Saudi border guards have fired "explosive weapons" on Ethiopian migrants trying to cross through Yemen into the Gulf kingdom, killing hundreds since last year, Human Rights Watch said on Monday.

The allegations, which Riyadh did not immediately comment on, point to a significant escalation of abuses along the perilous "Eastern Route" from the Horn of Africa to Saudi Arabia, where hundreds of thousands of Ethiopians live and work.

"Saudi officials are killing hundreds of migrants and asylum seekers in this remote border area out of view of the rest of the world," HRW researcher Nadia Hardman said in a statement.

"Spending billions buying up professional golf, football clubs, and major entertainment events to improve the Saudi image should not deflect attention from these horrendous crimes."

The New York-based group has documented abuses against Ethiopian migrants in Saudi Arabia and Yemen for nearly a decade, but the latest killings appear to be "widespread and systematic" and may amount to crimes against humanity, it said.