Samsung Electronics and SK Hynix, South Korea’s two memory chip giants, are warning of a prolonged and severe global supply crunch, weeks after the two companies disclosed increased investments in their China wafer fabs to meet surging artificial intelligence demand.

During Samsung’s first-quarter earnings call on Thursday, the company said its order fulfilment rate had plunged to a “record low”. In a rare move, customers worried about shortages were already pre-booking memory capacity for 2027,...