The first ODI between South Africa and England has again been called off at short notice after two members of the touring party received "unconfirmed" positive tests for Covid-19. England's players and staff are now self-isolating, with the abandonment casting fresh doubt on the feasibility of the series.

The first of three ODIs was due to be played in Cape Town on Friday, but was postponed less than an hour before the toss after a South Africa player tested positive for Covid-19.

On Sunday morning, ahead of the rescheduled opener in Paarl, CSA and the ECB released a joint statement 20 minutes before the scheduled toss confirming that the game's start time had been delayed. Two positives cases had been recorded among staff at the Vineyard Hotel, where both teams are staying, and England were re-tested on Saturday evening as a result.

Another joint statement was then issued, confirming that two members of England's touring party had "returned unconfirmed positive tests", with the fate of the series waiting on further advice from the relevant medical teams.

The statement said that a decision on the remaining matches in the series - scheduled for Monday and Wednesday - would be taken "once the results of the tests are ratified by independent medical experts" but with England due to leave on a charter flight on Thursday, December 10, it seems increasingly unlikely that the series will take place, an outcome that could have major ramifications for CSA

ESPNcricinfo understands that the two members of the England camp who returned positive tests will undergo further medical examination to determine the accuracy of the results.

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Graeme Smith, CSA's director of cricket, said: "We are deeply regretful of the situation we find ourselves in after the amount of time and energy that has been put in place to host a successful tour. We are in continuous talks with the ECB as we navigate the situation under the guidance of our combined medical teams."

Ashley Giles, the ECB's managing director for men's cricket, said: "We regret that we are unable to play in today's ODI, but the welfare of the players and support staff is our primary concern and whilst we await the results of further tests the medical advice from both teams was that this game should not take place.

"We remain in constant dialogue with Cricket South Africa and will continue to work closely with them to determine how best to move forward."

This is the fourth Covid-related incident on the tour, and the first involving England. South Africa had one member of their squad test positive before they entered the bio-secure bubble and another two days into their preparation. The first player did not stay at the same hotel as the teams and was placed in isolation, with two others who were deemed close contacts, and the second was removed from the hotel when he tested positive.

Then, on Thursday, ahead of the ODI series, another South African player tested positive and the first ODI was postponed less than an hour before the scheduled start. Now, the rescheduled first ODI has been cancelled.

Roy Davies, the Vineyard Hotel's general manager, issued a statement saying it was "unclear" how either staff member had been infected with the virus. It is understood, however, that not all hotel staff have been staying on site.

"Neither [staff member] has left the bio-secure area since November 16 and they do not work on the same team or in the same area," Davies said. "Our Covid response team is endeavouring to establish all the facts and contact tracing is underway. Our number one priority is the safety and wellbeing of our staff and guests and we have placed all our resources and efforts into investigating and resolving the situation.

"Both members of staff and a player who also tested positive on Friday are currently isolated in on-site apartments some distance from the hotel, which have been kept sterilised and available for this purpose. We will issue further statements as more facts become available."

With Sri Lanka, Australia and Pakistan all due to tour this summer, there will be major concerns within South African cricket about Sunday's abandonment, after England had expressed worries about the integrity of the bio-secure environment on Friday.