The World Health Organization has announced measures to fight the global spread of infectious diseases such as Sars and bird flu.
Diseases like the Sars virus have prompted the new rules
Countries will be obliged to apply stricter controls at ports and borders in the event of an outbreak.
Nations must also alert the WHO when a disease strikes, and respond to the agency's questions.
The new rules will be backed by international law, but do not specify penalties for non-compliance.
The regulations will also empower the WHO to restrict worldwide travel and commerce to and from affected areas.
WHO officials say the measures announced at the annual meeting in Geneva will give them much greater authority in demanding that countries be open about disease developments.
"This is a major step forward for international health," said WHO Director-General Lee Jong-wook.
"These new regulations recognise that diseases do not respect national boundaries. They are urgently needed to help limit the threats to public health," he said.
WHO offices around the world already provide support to countries in identifying and responding to disease outbreaks. But the WHO's head of disease surveillance, Guenael Rodier, said: "The existing regulations were written for a very different world from the one we live in today.
"Air travel was a luxury and the movement of goods and people around the world was relatively slow. Today, travel and trade have expanded far beyond what was envisaged under the original regulations."
New rules were drafted in 2003 after the outbreak of new infectious diseases, such as Sars, Ebola and bird flu, made the international community more wary of worldwide pandemics.