The embassy was evacuated on Friday afternoon when the ordnance was found by workers digging in the grounds of the mission, said embassy spokeswoman Rebecca Thompson.
By Saturday morning, experts had carefully removed 60 of the rusted and mud-covered rounds and transported them to a police base.
"They got everything that was found there," Thompson said, adding the US embassy grounds facing Manila Bay were used as the main headquarters of Japanese military forces from 1942 to 1945.
"It's not surprising to find those old bombs inside the compound, but we appreciate the quick response from Philippine authorities. They quickly and safely removed them."
Leopoldo Bataoil, Metro Manila police chief, said the ordnance was potentially lethal.
"Those bombs could still kill and create massive destruction," he said.
"There are sets of standard operating procedures we follow in properly disposing of these materials. We will examine these and take them to an area north of Manila where these will be properly detonated."
Police said reports of unexploded ordnance being found at construction sites in the capital remained common more than six decades after the end of World War II.
Manila, which was occupied by the Japanese military and then retaken by Allied forces, saw fierce fighting and was heavily bombed during World War II.