The regulations, adopted by the UN agency's 192 member states after two years of negotiations, oblige countries to tighten up disease detection and set guidelines for international measures to be taken.
In future, the WHO must be quickly informed of any outbreak of four diseases -- two new threats identified in Asia, Severe Acute Respiratory Syndrome (SARS) and bird flu, and two traditional virulent viruses, smallpox and polio.
Any "potential international public health concern," including outbreaks from unknown causes or sources and potentially deadly sicknesses such as cholera and yellow fever, must also be reported when they are sufficiently serious.
China, which was the source of the 2003 SARS outbreak which spread to 30 countries and killed 800 people, was accused of being slow to inform the WHO and neighbouring countries of what was at the time a new disease.
"The assembly has taken a bold and necessary step towards enhancing international cooperation in promoting and protecting global public health from all disease risks, irrespective of origin or source," a spokesman for UN Secretary-General Kofi Annan, Stephane Dujarric, said.
Dr. Lee Jong-wook, WHO Director-General, said the rules recognised that diseases do not respect national boundaries and were urgently needed to help limit threats to public health.
Previous guidelines drawn up in 1969 required countries to report three diseases -- cholera, plague and yellow fever -- to the UN agency, but demanded little else.
In any disagreement between the WHO and a member state on the seriousness of an outbreak, the rules allow the head of the UN body to summon a committee of experts to make recommendations on tackling the health threat, which could include travel bans for people or goods.
The WHO can also take account of disease reports from sources other than the government concerned when making its assessments.
Officials said the rules, which could help the world prepare for a long-predicted influenza pandemic, did not so much break new ground as put what had been established practice on a formal footing.
"What went before was ad hoc, nobody could be held responsible," said Irish diplomat Mary Whelan, who chaired the negotiations on the new regulations.
Any state imposing what others consider "inappropriate restrictions," such as holding up cargo or passengers, must justify their actions.
"You can be asked to justify on a scientific basis the reason for having applied those restrictive measures," said Max Hardiman, WHO's coordinator for the new health regulations.
Although the regulations do not mention specifically biological or chemical agents, as the United States had wanted, health officials said these were covered by the requirement to report any serious threat to international health.