About 1,200 military doctors and staff will work in the hospitals, which have a total of 140 beds. They will stay open around the clock.

In addition, 500 more troops will be deployed in the streets to help eradicate the dengue mosquito.

Among those turning up at a field hospital on Monday was Jorge Luiz Carvalho Alves. He had taken his 6-year-old daughter to four public hospitals only to find long lines. Over the weekend, a private clinic diagnosed her with the potentially lethal hemorrhagic form of dengue.

Alves said he had to borrow money to pay for the private consultation but it did not include treatment so he brought her to the field hospital's intensive care unit.

"Apparently she is in bad shape and will be hospitalised," he said, tears in his eyes, outside the camouflaged tents of an air force field hospital in Barra da Tijuca neighbourhood. "Many people, many children will die still if it's left to public hospitals."

Dengue is a viral disease spread by the Aedes aegypti mosquito and there is no vaccine or drug for it. Treatment primarily involves increased fluid intake, administered orally and intravenously.

It has various strains, including one that causes the hemorrhagic form. It tends to affect people who previously have contracted a weaker strain.

'HERE IT'S WONDERFUL'

The waiting lists at military hospitals were short on the first day and triage efficient.

"In the hospital you wait and wait and people have no respect for you. Here it's wonderful," said Ana da Silva Henrique, a 29-year-old cleaning maid who took a bus for 90 minutes to get to a field hospital on Monday morning.

She was put on an intravenous drip an hour after coming. At a public hospital near where she lives, she had waited in line for four hours and been sent home with pains and fever after a quick consultation.

Authorities have deployed cars equipped with powerful insecticide sprays and were checking areas with pools of stagnant water where mosquitoes can breed.

Last week, Health Minister Jose Temporao blamed a poor disease prevention network and fragile public health system for the crisis.

In 2005, the military also set up field hospitals in Rio after a breakdown in the state public health system led to long lines at hospitals.

Authorities hope the outbreak will ease in the coming weeks with the arrival of cooler weather after a hot, wet summer.

Most of the affected areas are relatively far from tourist districts, but no one is completely safe from the mosquito-borne disease.