Catalysis of the reaction: 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine + ATP = (2-amino-4-hydroxy-7,8-dihydropteridin-6-yl)methyl diphosphate + AMP + 2 H+.
2-amino-4-hydroxy-6-hydroxymethyldihydropteridine pyrophosphokinase activity