The Brazilian ministry of health has declared a nationwide public health emergency while doctors investigate whether a mosquito-borne disease that is new to the country is behind a sudden spike in the number of babies born with abnormally small heads.
The Zika virus is one of several possible causes being considered after one region saw a 15-fold increase in cases of microcephaly, a congenital abnormality that causes an infant's head to measure less than 33cm. Normally, the head circumference of a newborn is between 33cm and 38cm.
Depending on the severity of the condition, babies born with microcephaly often develop with cognitive problems or other developmental issues including impaired motor functions, coordination, and speech. The prognosis varies, but life expectancy is typically lower than average.
In the northeastern state of Pernambuco there have been 141 babies born with the condition so far this year, compared with a normal average of nine per year. A hospital in Recife, the state's capital, attended six of the babies on Thursday morning alone.
A health ministry spokeswoman told VICE News that the emergency alert, issued on Wednesday, was intended to channel resources for investigating the situation as a matter of urgency. She said a rapid response team was deployed to Recife to carry out clinical tests last month, when the government was first notified of the increase.
Guidelines issued by the ministry on Friday recommended that pregnant women in the northeast of Brazil attend all relevant prenatal tests and examinations, avoid alcohol and drugs, and take measures to reduce the risk of mosquito bites.
"Until the causes behind the increase in cases of microcephaly in the northeast are clarified, women who plan to become pregnant should talk confidentially to a health team. In this consultation, information and risks to the pregnancy will be evaluated to help you take your decision."
The ministry said it would be releasing an update on the situation next Tuesday.
Two other northeastern states neighbouring Pernambuco have also reported higher than usual rates of the condition that is caused by impaired brain development.
Dr Kleber Luz, an infectologist at the Federal University of Rio Grande do Norte, said there have been 22 cases of microcephaly in the state capital Natal this year compared to an average of four. He said 80% of the mothers reported symptoms suggesting they had contracted the Zika virus during the first trimester of their pregnancy.
"When the virus arrived in Natal, it surprised everyone and a lot of people got sick," he told VICE News. "It's very serious. It's something new for the scientific community and we are having meetings to investigate."
He stressed, however, that there is still no clear clinical evidence linking the condition to the virus. According to the health ministry the virus originated in Uganda and arrived in Brazil last May.
The infection is similar to dengue fever though the symptoms are less serious. They typically include high fever, a rash, and inflammation of the eyes. Patients usually recover within a week with treatment limited to painkillers and drugs to reduce the fever.
Other possible causes of the rising number of cases of microcephaly suggested so far include dengue, genetic factors, or substance abuse by the mothers.
While the phenomenon currently appears to be concentrated in the northeast, local health ministries elsewhere in the country have also announced they are on alert.
The Rio de Janeiro health authorities said they would be retrospectively investigating cases of microcephaly and reviewing reporting procedures for the future.
"We start these new protocols next week," said Rio's undersecretary of public health, Alexandre Chieppe. "We are anticipating this situation in Rio."
Meanwhile, the state government in Pernambuco said it was organising support groups for pregnant mothers who already know their babies have microcephaly and mothers of newborns with the condition.
"For us, it's very new. This has never happened before. It's a war operation," said Luciana Albuquerque, executive secretary for health surveillance in Pernambuco. "It's as much about receiving and supporting as knowing the cause."
One mother whose daughter was born with microcephaly a month ago told the news website G1 that she had a suspected case of dengue while she was pregnant.
"There were many doubts and we didn't know what caused it. It would scare anyone," she said, her identity withheld. "Now we are seeking out information and understanding what microcephaly is."
Follow Donna Bowater on Twitter: @donnabow