Saudi Arabia confirmed one cholera case and said three others were suspected in an area bordering Yemen, where an epidemic has killed more than 2,000 people, Saudi state TV said, citing a health ministry official.
The report late on Sunday said the patients, identified only as non-Saudis, were receiving care at al-Mauwassem General Hospital in Jizan, about 1,000 km (620 miles) southwest of the capital, Riyadh.
It was unclear if the outbreak was linked to Yemen or to last month's Muslim haj pilgrimage, which draws some two million foreigners each year, raising the risk of the spread of infectious disease.
Saudi Arabia reported five cases of cholera in 2017, all of which were imported, and there was no further spread, according to the World Health Organization (WHO).
The WHO said on Monday the origin of the current cases was not yet known but the outbreak was not expected to spread given Saudi Arabia's infrastructure.
"Infectious diseases have no borders, and cholera is no different," spokeswoman Fadela Chaib told Reuters.
"Saudi Arabia has extensive measures in place to manage health issues during the haj, and has been able to prevent outbreaks by making sure that pilgrims to the haj have adequate water, sanitation, and hygiene facilities."
The incubation period for cholera, which spreads through ingestion of faecal matter and causes acute watery diarrhoea, is a matter of hours. Once symptoms start, it can kill within hours unless the patient receives treatment.
The WHO has rolled out an emergency treatment programme, based on the vestiges of Yemen’s shattered health system, to try to catch new cases early and stop the explosive spread of the disease.
Saudi Health Minister Tawfiq al-Rabeeah said last month that the haj had passed without any outbreak of disease.