CONCEPCION, Chile — Huge piles of wreckage and tons of rotting fish and other debris blanketing the ground could turn coastal towns shattered by Chile’s earthquake and tsunami into nests of infection, doctors warned.

As calls for medicine and shelter grew, U.N. Secretary-General Ban Ki-Moon flew into the heavily damaged city of Concepcion aboard a Chilean air force plane Saturday, following at least six moderate aftershocks. He was driven immediately to the city’s ground zero, where a 15-story apartment building had split and collapsed, killing at least nine, according to firefighters.

Authorities moved to demolish the wrecked building as one couple took one last walk through the rubble, calling out in vain for their missing son, Jose Luis.

“Remember that we are with you … our hearts are with you,” Ban told reporters in a brief statement outside the building, constructed only two years ago.

Ban said the U.N. will discuss how best to mobilize aid to Chile at its next General Assembly meeting, whose date has not been set. Meanwhile, the country will receive field hospitals, temporary bridges and other international aid that the Chilean government needs, the secretary-general said later after returning to Santiago.

A week after the magnitude-8.8 earthquake, hundreds of people were still searching for their loved ones through the local radio station, where messages run day and night.

As Chileans mounted an extensive vaccination campaign, doctors said cases of diarrhea are increasing from people drinking unclean water, and a growing number of patients are suffering injuries wading through the mess.

“We are going to keep needing water, electric systems, a functioning sewage system. We need to clean up rotting fish in the streets. We need chemical toilets, and when it starts raining, people living in tents are going to get wet and sick. All this is going to cause infections,” said Talcahuano Mayor Gaston Saavedra, whose port city was heavily damaged by the Feb. 27 quake and tsunami.

But the Chilean Health Ministry said that there had been no outbreaks of dysentery or other communicable diseases so far, and it has enough tetanus and hepatitis vaccinations for the disaster zone.

The government faces other health-care problems. Looting of pharmacies has made medicine scarce for people suffering from diabetes, hypertension and psychological illnesses, and 36 hospitals were heavily damaged or destroyed in the quake.

Chile said more than a dozen of its own military and civilian field hospitals were operating by Saturday. Mobile hospitals from a half-dozen other countries also were opening or about to open — an unusual situation for a country that proudly sends rescue and relief teams to the world’s trouble spots.

But most of the foreign units weren’t treating anyone a week after the disaster. Chile insisted donor nations first figure out how to coordinate with Chile’s advanced, if wounded, public health system.

Luis Ojeda, a Spanish doctor working with Doctors Without Borders, said his team arrived Monday but was still waiting for Chile’s instructions on where to deploy.

Chile signed an operating agreement for a U.S. field hospital Friday, enabling 57 U.S. military personnel to work side-by-side with civilian Chilean doctors in the town of Angol.

In Rancagua, a Cuban field hospital was fully operational.