The first ODI between South Africa and England in Cape Town has been called off, less than an hour before the toss.

As reported by ESPNcricinfo, the postponement related to a further positive Covid-19 test within the South Africa camp, amid suggestions that protocols had been breached during the T20I series.

All players and support staff are set to undergo another round of tests on Friday evening, in the hope of starting the series on Sunday.

A CSA statement said: "This decision results from a player from the Proteas team testing positive for Covid-19 after the teams' last round of scheduled testing performed on Thursday ahead of the ODIs.

"In the interests of the safety and well-being of both teams, match officials and all involved in the match, the acting CEO of CSA, Kugandrie Govender as well as the CEO of the ECB, Tom Harrison, have agreed to postpone the first fixture to Sunday."

The news emerged as the England team bus arrived at Newlands to begin their preparations for the match, whereupon the players immediately returned to the teams' bio-secure base at Cape Town's Vineyard hotel.

A contingent of South Africa players and support staff later arrived for a short net, including David Miller and Andile Phehlukwayo, who are understood to have been the two players who had previously tested positive for Covid-19. Both were keen to increase their workloads after missing the T20I series, however, they were soon instructed to return to the team hotel by CSA.

CSA and the ECB now hope to stage the three games on Sunday, Monday and Wednesday. The first game will take place at Paarl, with the second and third fixtures under lights at Newlands in Cape Town.

Govender, CSA's acting CEO, confirmed the news to ESPNcricinfo. "The doctors on both sides have told us that it is a perceived risk and not an actual risk, but both boards have decided that we would rather have the players not go onto the field if there is any kind of risk at all," she said. "Everybody will be tested again today and there is a 24-hour turnaround for results."

Asked what would happen if there were more positive cases, Govender said that the board would seek further medical advice, but insisted that the infected player had not come into contact with any others. A CSA spokesman later added that the board was "not aware of any protocol breach".

The Western Cape, where both Cape Town and Paarl are situated, has seen a resurgence in Covid-19 cases in the last few days, and as of Thursday, the region had 10,000 active cases.

Three positive tests have now been recorded in the South African camp, and CSA's chief medical officer Dr Shuaib Manjra had previously flagged that the schedule could be affected if more players returned positive tests.

Although the player or players in question cannot be confirmed by CSA due to doctor-patient confidentiality, it is understood that the England camp has been unsettled by the protocol breaches, and the players may be reluctant to agree to the rescheduling. Plans to hold a joint press conference between CSA and the ECB were cancelled, with Ashley Giles, England's team director, putting out a statement instead.

"On behalf of the England touring party and the ECB, I would like to thank Cricket South Africa for their collaborative approach to postponing today's one-day international," Giles said. "Our number one priority is the health and safety of the England team and management group, and the correct decision was made following discussions between the two boards and respective medical teams.

"The England party will remain at its base in Cape Town on Friday and Saturday, and we are hopeful that the three-match series will be played before we depart next Thursday, starting with the match at Paarl on Sunday."

The England squad is due to fly out of South Africa on a chartered flight on December 10, with several players also due to link up with their franchises for this year's Big Bash League in Australia - and there are understood to be concerns within the squad about jeopardising those plans unnecessarily.

A further complication could arise with the speed at which the latest round of tests are returned. It is understood that Thursday's batch were returned after 11pm on Friday, meaning that a similar timeframe over the weekend could have implications for Sunday's rescheduled fixture.

George Dobell is a senior correspondent at ESPNcricinfo