Car inable to get up steep hill

Was driving up a hill with 4 occupants in car
Car slowed down to just about stopped, kept foot on throttle
And it kept going just. After about 50/60 yards started topickup spesd nesttopofhill after that seems to run okay. Any ideas shat it is could it be the clutch or could someghing else be the problem there wad a smell of burning for a while