Around 30 countries have health systems so weak they could not deal with an outbreak of a disease such as Ebola, WHO says.

About 30 countries have health systems that are as dangerously weak as the ones that allowed Ebola to ravage Guinea, Liberia and Sierra Leone, the World Health Organization has warned.

The UN health agency stressed the urgency of learning the lessons drawn from the outbreak that has killed more than 11,100 people in west Africa, calling for strengthening health systems so they can rapidly detect and counter looming disasters.

"We must reverse the trend in global health where we wait for the fire to flare up, run to put it out but then forget to fireproof the building," said senior WHO official Ruediger Krech on Thursday.

The world, he told reporters, had to create a health system "built to withstand shocks whether from an outbreak like Ebola, a natural disaster or a financial crisis."

The fragile health systems in Guinea, Sierra Leone and Libera, weakened by conflict and poverty, were an important factor in Ebola's rapid spread through the three countries last year.

And Krech said at least 28 other countries worldwide, mainly in Africa, but also in Asia and Latin America, had similarly weak systems.

The list includes Democratic Republic of Congo, Madagascar, Burundi, Sudan, Afghanistan and Haiti.

The Ebola outbreak began in late 2013 in Guinea, but was permitted to spread silently for three months before the WHO and the region raised the alarm.

The crisis sparked a global health scare, with the humanitarian response especially gaining momentum once stray cases were detected in the United States and some European countries.

Liberia, once the worst-hit country, was declared Ebola-free on May 9. But Krech said the crisis was far from over in the two neighbouring countries and refused to give a timeframe for them to acquire a similar status.