(at) full speed, (at) full pelt, as fast as one's legs can carry one, at a gallop, helter-skelter, headlong, hotfoot, post-haste, hurriedly, hastily, wildly, pell-mell, impetuously, recklessly, rashly, at breakneck speed, precipitately, impulsively

informal p.d.q. (pretty damn quick), double quick, at a lick, hell for leather, pronto, at the double, a mile a minute, like the wind, like a bomb, like a bat out of hell, like a scalded cat, like the deuce, like nobody's business, like (greased) lightning, like a madman/madwoman

British informal like the clappers, at a rate of knots, like billy-o

North American informal lickety-split

literary apace

archaic hurry-scurry

with great force, (with) full force, full blast, with a will, for all one is worth, with might and main, with all the stops out, all out, with a vengeance, vigorously, energetically, strongly, powerfully, madly

informal hammer and tongs, going great guns, like crazy, like mad

British informal like billy-o