Port-au-Prince, Haiti (CNN) — Much-needed medical reinforcement arrives in Haiti on Wednesday in the form of a state-of-the-art hospital aboard a U.S. naval ship.

The USNS Comfort, which saw duty in the aftermath of Hurricane Katrina in 2005 and the 2001 terror attacks in New York, is to arrive mid-morning in the flattened capital, Port-au-Prince. U.S. helicopters will ferry patients aboard, bringing relief to overloaded hospitals and clinics.

The area experienced a strong magnitude 6.1 aftershock Wednesday morning. The epicenter of the aftershock was 36 miles west-southwest of the capital and 6.2 miles deep, the United States Geological Survey said.

Before the aftershock, two severely injured Haitians were transported to the hospital ship as it sailed toward Haiti, according to the Department of Defense.

The patients — a 6-year-old boy with a crushed pelvis and 20-year-old man with a broken skull and possibly fractured cervical vertebrae — had been treated initially on the USS Carl Vinson, a U.S. aircraft carrier docked off the Haitian capital.

The Comfort is carrying nearly 550 doctors, nurses, corpsmen, technicians and support staff, who will be joined by 350 other medical staffers once the ship reaches Haiti, according to the U.S. Southern Command. The ship will have six operating rooms available and can house up to 1,000 patients.

The United States has been conducting some medical operations aboard the USS Carl Vinson, docked off Haiti’s coast.

More than a week after a 7.0-magnitude earthquake devastated the impoverished nation, efforts to get hospitals back into working shape were seeing some results, but the injured were still streaming in.

Surgeries resumed Tuesday at University Hospital, the country’s largest, said Dr. Jon Andrus, deputy director of the Pan American Health Organization (PAHO).

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At the general hospital in Port-au-Prince, doctors were working under stressful conditions in buildings located away from the main building, which has been deemed unsafe.

“We have run out of IVs and IV needles and IV fluids,” said Dr. Mark Hyman of the medical relief organization Partners in Health. “We’ve run out of surgical supplies. We have to wash with vodka and we have to operate with hacksaws because we don’t have enough operating tools.”

The military is going to help with organization and supplies, Hyman said. “They’re going to help us get electricity, they’re going to help us get food, they’re going to help us get tents, they’re going to help us get all the operating supplies in,” he said.

Early Wednesday, 3 million Haitians were still in need of food, water, shelter and medical assistance, the United Nations estimated.

And the death toll is expected to climb.

Authorities have buried about one-third of the estimated final toll. Prime Minister Jean-Max Bellerive told CNN’s Christiane Amanpour that at least 72,000 bodies had been recovered, not including the unknown number of bodies buried by families or collected by the U.N. peacekeeping mission in Haiti.

It was unclear how many of the dead had been identified before burial and how many of those burials occurred in mass graves. “We know that bodies have been buried, we feel inappropriately,” said PAHO’s Andrus. He cited lack of refrigeration as a complicating factor, and also made an urgent appeal for blood donors, because storage was not possible.

“Despite all our efforts, situations, circumstances are such that we are disappointed in many cases on how this has been managed, beyond everybody’s control,” he said.

PAHO, which is coordinating the health-sector response, offered a preliminary estimate of 200,000 dead.

At least 28 of them were Americans, the U.S. State Department announced Tuesday.

But miraculous rescues were still taking place Tuesday. Even after a week under the rubble, people were being pulled out alive.

A team of New York City Fire Department and Police Department rescuers pulled two children alive from the rubble of a two-story Port-au-Prince building Tuesday night. The 8-year-old boy and 10-year-old girl were taken to an Israeli tent hospital.

Earlier, rescuers pulled a survivor from the rubble near Haiti’s national cathedral. Rescue crews said two other survivors might be under the same pile, though hopes faded in the evening.

In all, international rescue teams composed of about 1,700 people have rescued 121 people, the United Nations said.

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Outside Haiti, people have contributed more than $220 million to major U.S. relief groups, according to The Chronicle of Philanthropy, a newspaper covering nonprofit organizations. But the world’s generosity continued to overwhelm the ability of the airport in Port-au-Prince. The result: Some badly needed aid was left sitting on the tarmac.

U.S. Army Maj. Daniel Allyn, the deputy commander of the Joint Task Force Unified Response, said flights would be diverted to two alternate ports of entry within the next day or two to relieve the pressure. On an average day before the earthquake, the airport was handling 13 commercial aircraft; in the days since, it was handling more than 200, he said.

Some flights were diverting to Santo Domingo, causing congestion there, too, Andrus said.

Nevertheless, advances were being made: Many roads that were impassable in the initial aftermath of the quake had been cleared, so that supplies could be trucked to those in need, he said.

In Washington, U.S. Agency for International Development Administrator Dr. Rajiv Shah told reporters Tuesday night that the U.S. response has been “swift, aggressive and coordinated.”

He cited the U.S. donations of 18 water production units providing nearly 2 million liters of drinking water per day and nearly 17 million meals as examples.

The goal of the efforts, he said, “is to make sure that the things we do collectively as an international community to support the relief effort are as sustainable as possible.”

In an interview with CNN’s Amanpour, Haitian President Rene Preval applauded the progress aid workers have made over the past week in restoring electricity and communication, clearing roads, erecting shelters, distributing food and re-establishing hospitals.

He credited the international community.

“Without their help, it would be impossible for us to cope with the situation,” he said.

The U.N. Security Council approved sending an additional 2,000 soldiers and 1,500 police officers to the country and the port is expected to reopen next week, said U.N. Secretary General Ban Ki-moon.

Fixing the port is a priority, because it is where fuel enters the country. Venezuela’s President Hugo Chavez announced Sunday that he will send 225,000 barrels of gasoline and diesel, with arrival Thursday at a refinery in the Dominican Republic, for use in Haiti.

That represents nearly three weeks worth of fuel if Haiti were to continue the 11,000 barrel-per-day consumption that was typical before the earthquake.

About 2,000 U.S. troops were in Haiti, and more than 5,000 were off-shore on ships, Allyn said. The U.S. military anticipated eventually having 10,000 troops in Haiti, he said.

Some Haitians welcomed the arrival of U.S. forces, but one man said Haitians needed more relief supplies, not troops or guns.

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