Hundreds of people, many of them Ethiopians who cross war-torn Yemen to reach Saudi Arabia, have been shot dead.
Migrants says they had limbs severed by gunfire and saw bodies left on the trails.
Saudi Arabia has previously rejected allegations of systematic killings.
The Human Rights Watch report, titled they Fired On Us Like Rain, contains graphic testimony from migrants who say they were shot at and sometimes targeted with explosive weapons by Saudi police and soldiers on Yemen's rugged northern border with Saudi Arabia.
Migrants contacted separately by BBC have spoken of terrifying night-time crossings during which large groups of Ethiopians, including many women and children, came under fire as they attempted to cross the border in search of work in the oil-rich kingdom.
A migrant says some in his group of 45 migrants were killed when they came under fire as they tried to sneak across the border in July last year.
He adds he didn't even notice he was shot, but when he tried to get up and walk, part of his leg was not with him.
Mustafa Soufia Mohammed says he came under fire at the Saudi-Yemeni border it was a brutal, chaotic end to a three-month journey fraught with danger, starvation and violence at the hands of Yemeni and Ethiopian smugglers.
