South Africa on Tuesday suspended the rollout of the Johnson & Johnson COVID-19 vaccine over potential blood clot risks reported by the United States, the health minister said.

The announcement delays an already sluggish vaccination campaign in Africa's worst-hit country, which has so far only administered the US-made jab.

"We have determined to voluntarily suspend our rollout until the causal relationship between the development of clots and the Johnson & Johnson vaccine is sufficiently interrogated," Health Minister Zweli Mkhize said in an online briefing.

Earlier Tuesday, the US Food and Drug Administration (FDA) and the Centers for Disease Control recommended a pause in the use of the single shot J&J vaccine over potential links to a rare type of blood clot.

The US agencies said they were acting "out of an abundance of caution", but J&J has since delayed the rollout of its jab in Europe.

Mkhize said that although no blood clots had been reported among vaccinated citizens in South Africa, the FDA's advice should not be taken "lightly".

"We hope that the deliberations will only take a few days," he added. 

"Given the preliminary literature at hand, our scientists are confident that the FDA decision is only on a precautionary basis, and we expect that this will not result in the complete withdrawal of the Johnson & Johnson vaccine."

- Pfizer back-up -

South Africa has vaccinated just under 290,000 health workers since February 17.

The second phase of the country's rollout plan, which will target essential workers and the over-60s, is scheduled to begin on May 17.

Officials had already been forced to scrap plans to start vaccinating with the Oxford/AstraZeneca jab after a study suggested the formula was less effective against a dominant local virus strain.

So far, South Africa has secured 31 million doses from J&J and 30 million from Pfizer, a first batch of which is scheduled to be delivered in early May.

Another 1.2 million doses will be donated by the international vaccine sharing facility Covax, and an undisclosed amount from the African Union.

South Africa has secured more than enough doses to vaccinate 40 million people -- roughly 67 percent of the population -- by the end of 2021, said Mkhize.

Even in the "extremely unlikely event" that the J&J rollout is "completely halted", the arrival of the Pfizer jabs would allow the second vaccination phase to begin on time, he added.

The latest developments "provide comfort that medical authorities keep a vigilant watch on new products", he argued, calling on citizens to remain calm and patient.

South Africa's coronavirus outbreak has remained relatively stable since a second surge in infections during December, although experts warn of a looming third wave over the upcoming southern hemisphere winter. 

To date the country has reported over 1.5 million coronavirus cases, and 53,356 deaths.   

South Africa accounts for more than 35 percent of all infections recorded in Africa, according to an AFP tally.