Huge piles of wreckage and tons of rotting fish and other debris are turning the coastal towns shattered by Chile's earthquake and tsunami into nests of infection, doctors have warned.

As Chileans lined up for hepatitis and tetanus shots on Friday on the opening day of an extensive vaccination campaign, doctors said cases of diarrhoea were increasing from people drinking unclean water and a growing number of patients were 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 last month's quake and tsunami.

The government faces other healthcare 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 on Friday. Mobile hospitals from half a dozen other countries were opening or about to open. 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 public health system.

Chile signed an operating agreement for a US field hospital on Friday, enabling 57 US military personnel to work side by side with civilian Chilean doctors to support a population of 3,000 in the town of Angol. Two US transport planes were en route to Chile to help deliver supplies.

Chile's health ministry said that there had been no outbreaks of dysentery or other communicable diseases and that it had enough tetanus and hepatitis vaccinations for the disaster zone.

Powerful aftershocks on Friday forced the evacuation of an older wing of Concepción's five-storey regional hospital.

The emergency room supervisor, Dr Patricia Correa, said her part of the hospital "is on the point of collapsing. The walls cracked".

The most powerful aftershock in six days sent terrified Chileans fleeing into the streets. The 6.6 shock at 8.47am rattled buildings for nearly a minute.

Chile's health ministry said its top priorities included mental healthcare for quake survivors, garbage removal, drinking water and shelter. Housing minister Patricia Poblete said at least 500,000 homes were destroyed but she expected that figure to reach as high as 1.5 million once surveys were complete.

In New York, Chile's UN ambassador, Heraldo Munoz, said reconstruction would cost Chile an estimated €22bn.

Officials struggled to determine the death toll. Disaster officials announced they had double-counted at least 271 missing as dead – an error that would drop the official death toll to about 540 without other mistakes. Interior Department officials said they would now release only the number of dead who had been identified: 452 as of late Friday.

In Santiago, UN secretary-general Ban Ki-moon promised quick aid deliveries to President Michelle Bachelet and president-elect Sebastian Pinera.