Soldiers began putting up a network of sturdy tents on open ground just to the south of Muzaffarabad to house two 12-bed intensive care and surgical units.
"We're going to be able to perform surgery by this evening," said Lieutenant Kevin Stephens of the Germany-based 212th MASH.
On Tuesday, the unit treated two children who were hurt in the October 8 quake which killed more than 53,000 people and injured over 75,000 seriously.
"This morning, these folks turned up at the gate so we showed them in," Stephens said of the two children and their parents.
Both of the children had already been treated - the young girl had a broken leg in a cast and the boy had an injured foot - but they were both given X-rays and additional care.
Nobody knows what the final death toll will be after the most violent earthquake Pakistan has ever suffered, with uncounted bodies still lying under the rubble of mountain villages.
The number of injured is also likely to soar, with people still being brought down by helicopters after they drop relief supplies or carried down from villages the aircraft cannot reach more than two weeks after the quake.
The harsh Himalayan winter is only a few weeks away and about 3 million people are homeless.