- We've seen a doubling of cases over the last week," Dr Julie Hall, the Red Cross federation's director of health and care, told reporters in Geneva.
- Red Cross officials have said the situation is particularly worrying because pneumonic plague, which is spread from person to person, has occurred for the first time in non-endemic areas and crowded cities.
- About 70 percent of the cases are the pneumonic form.
- A total of 12 people showing plague-like symptoms in The Seychelles
The World Health Organization said 567 cases have been reported so far, with another in the Seychelles.
"The situation, as you know, is quite concerning.
About 70 percent of the cases are the pneumonic form.
Cases of bubonic plague, transmitted from animals to people through flea bites, occur almost annually in Madagascar.
The rise in cases is due in part to a stronger reporting system, and not all cases have been confirmed, Hall said.
Fears are growing that the outbreak will spread to other countries.
Authorities in Seychelles this week said a man was diagnosed with pneumonic plague after returning from Madagascar.
The outbreak began after the death of a 31-year-old man in Madagascar's central highlands in late August.
The Seychelles government ordered schools to close Friday after the discovery of two suspected cases of plague thought to have been brought from Madagascar where the disease has killed scores. The health ministry has also put under surveillance 320 people who have come into contact with the two patients.
A total of 12 people showing plague-like symptoms have been admitted to hospital and given antibiotics.
Panic gripped parents on the Indian Ocean archipelago after some students developed fevers in recent days, leading to the school closures.
"It has not yet been confirmed that the two people are sick due to the plague, samples will be sent this weekend to the Institut Pasteur (in France)," said public health commissioner Jude Gedeon.
The results are expected next week.
Plague outbreaks are common on Madagascar, 1,800 kilometres (1,120 miles) to the south, where the disease is endemic.
But this year both bubonic plague, spread by infected rats via flea bites, and the pneumonic type, spread person-to-person, have hit urban areas, including the capital Antananarivo, leaving at least 54 dead.