"WHO is now recommending as a measure of precaution that people planning to travel to Tianjin and Inner Mongolia provinces of China and Taipei in Taiwan ... consider postponing all but essential travel," said a statement by the U.N. agency.
The agency has already issued travel warnings for Hong Kong (search), Beijing and China's Guangdong and Shanxi provinces.
The WHO lifted a similar warning on nonessential travel to Toronto on April 30 after deciding the disease had been sufficiently contained by health authorities in the Canadian city.
WHO said it would likewise regularly reassess whether to change its travel advice for the other areas.
It said it had "carefully reviewed" the information about the SARS outbreaks in Tianjin, Inner Mongolia and Taipei.
"The travel advice is based on a consideration of the magnitude of the outbreaks in these regions, including both the number of prevalent cases and the daily number of new cases."
WHO said the extent of "potential spread" was also taken into consideration.
WHO said so far there are more than 7,000 SARS cases in 29 countries on five continents and that much of it was spread "along the routes of international air travel."
It said precautionary measures helped reduce the impact of SARS and contained the disease in an early stage.
"National authorities have heightened surveillance for suspect and probable cases," WHO said. "In many countries, prompt detection and isolation of initial cases have prevented further transmission altogether or held additional cases to a very small number."