JOHANNESBURG - Some South Africa hospital wards are jammed with patients infected with the omicron coronavirus variant as President Cyril Ramaphosa urged South Africans on Monday to get vaccinated.

In the past week, cases have reached more than 16,000, up dramatically from 2,300 last Monday, according to South Africa's National Institute for Communicable Diseases.

The NICD says the increase in cases in such a short period of time is "unprecedented" in the trajectory of the pandemic, now in its fourth phase in the country.

"Unfortunately, we're seeing a more than doubling of hospital admissions each day," said Ian Sanne, an infectious diseases specialist who serves on South Africa's COVID-19 presidential advisory committee.

Sanne is advising hospitals to prepare for "significant surges" of patients in the coming weeks and months, and to make sure they have plenty of oxygen.

Dr. Fareed Abdullah, who heads the South African Medical Research Council, says the surges are already happening in Johannesburg and Tshwane.

Hospitals in South Africa's Gauteng province, which contains two of the country's biggest cities, are packed with people infected with the omicron variant. Doctors say most of the patients haven't been vaccinated, and an alarming number of them are children under the age of five-years-old.

"There's been a rather rapid rise in hospital admissions with patients who have COVID, whether they're presenting with COVID pneumonia or severe COVID disease,' Dr. Abdullah said.

'All of the hospitals in Tshwane are seeing an upsurge, and the COVID bed occupancy is increasing 30% to 40% per day, over the last few days," he said.

Some 36% of South Africans are fully vaccinated and President Ramaphosa on Monday urged citizens to get the shots.

'South Africa now has sufficient supplies of vaccines, ... vaccination is essential for our economic recovery because as more people are vaccinated more areas of economic activity will be opened up,' he said.

The president also announced that that the National Coronavirus Command Council would soon meet to discuss further measures. Authorities are considering making vaccines mandatory in some parts of society.

Unvaccinated people are particularly susceptible to omicron, as are individuals who have not been exposed to COVID-19 before, disease specialist Sanne said.

"At this time, we think about 75% to 80% of hospitalizations are unvaccinated,' he said. 'It could be as large as 40% of the population that has not yet either been vaccinated or had a previous infection with coronavirus up until now," he noted. "So, we have a large pool of people who can still present with overwhelming infection and severe disease," he said.

Since detection of the variant was first announced in southern Africa last month, scientists have been hoping that most cases would be mild.

Health authorities say omicron is re-infecting some people who have been vaccinated, but mostly their symptoms are not severe.

One of the country's top epidemiologists, Salim Abdool Karim, told VOA that current vaccines should provide "good protection" against omicron.

Another disease expert, Shabir Madhi, noted, however, that the longer viruses flourish in populations, the more likely they are to mutate into variants.

"Without any question, if we were to vaccinate more people, we'd be able to dampen the amount of virus that would be circulating,' Madhi said. 'We're not going to eliminate this virus, by any stretch of the imagination.

'But we can reduce the amount of virus that's circulating and most importantly, vaccines are going to be much more foolproof when it comes to protecting against severe diseases, than taking your chances without being vaccinated," Madhi said.

Disease specialist Sanne said that COVID-19's going to be around for a "long time" to come, and those who believe the disease will eventually "just fizzle out," are wrong.

'We don't have the ability to predict that this virus as a virus becomes weaker, whereas we do in fact see that the immune system will improve with time to in fact deal with the infection," he said.

Reuters contributed to this report.