as fast as possible, as quickly as possible, very fast, very quickly, very rapidly, very speedily, very swiftly, hurriedly, at full speed, at the double, at full tilt, at full pelt, headlong, hotfoot, post-haste, pell-mell, helter-skelter, at the speed of light, at breakneck speed, like an arrow from a bow

informal like a bat out of hell, at a lick, like the wind, like greased lightning, at warp speed, like a bomb, like mad, like crazy, like blazes

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

North American informal lickety-split

literary apace, hurry-scurry