A spokesman for Argentina's president says Cristina Fernandez was awake and recovering after surgeons removed her cancerous thyroid gland.

Alfredo Scoccimarro said the surgery Wednesday took 3.5 hours and that doctors removed the entire thyroid gland, without any complications. He said the president's doctors also predict a speedy recovery, and that she should stay in the hospital for 72 hours.

Supporters outside the Hospital Austral in suburban Pilar, north of the capital of Buenos Aires, erupted in cheers and applause at the news.

Vice-President Amado Boudou was put in charge shortly before the operation, and will remain as constitutional leader for 20 more days while Fernandez takes medical leave, the presidency said.

Fernandez, 58, was found to have papillary thyroid carcinoma shortly after beginning her second four-year term as Argentina's leader last month, her doctors said.

Early Wednesday, Fernandez flew by helicopter from the presidential residence in Olivos to the Hospital Austral in suburban Pilar, north of the capital. She went under general anesthesia several hours later for the operation led by Dr. Pedro Saco, a veteran Argentine oncologist who specializes in cancers of the head and neck.

Medication needed for life after thyroid removal

Experts say thyroid removals are about as routine as cancer surgeries can be, although the process is not without risk: surgeons must take care not to damage a nearby nerve that guides the vocal cords, or to remove the adjacent parathyroids, which regulate the body's calcium supply.

Patients should generally take care to relax their necks after surgery. Temporary hoarseness is common, and in rare cases, permanent voice changes can result. Patients also must swallow radioactive iodide for several days to destroy any cancerous remnants and provide for clearer images to detect any additional cancer, according to the U.S. National Institutes of Health.

After surgery, patients take medication — levothyroxine sodium —  for the rest of their lives to replace a hormone produced by the thyroid gland. Blood tests every six to 12 months to measure thyroid levels also are recommended.

Fernandez's doctors said the tumour had not metastasized or spread beyond the nodule.

While the plan is for her to remain hospitalized for up to 72 hours, most patients recover quite quickly.

Other leaders underwent cancer treatments

Fernandez is only the latest sitting South American president to be diagnosed with cancer. The others, who also have undergone treatments, are:

  • Fernando Lugo of Paraguay.
  • Hugo Chavez of Venezuela.
  • Dilma Rousseff of Brazil.

Supporters waited anxiously outside the hospital for word on the surgery's results, waving flags, carrying handmade signs that said "Be Strong Cristina" and building small shrines to the populist leader, who won re-election with a 54 per cent landslide in October.

Many carried pictures showing Fernandez and her late husband, former president Nestor Kirchner, who died of a heart attack in 2010.

Boudou, her former economy minister, is expected to work closely with Fernandez's other cabinet members while she recuperates at her home in Calafate, in far-southern Argentina, and make no major policy changes. Argentina all but shuts down anyway for the summer holidays in January and February, so her diagnosis and surgery came at a relatively calm time.