A leading team has called for the Giro d'Italia to end one week early this coming Sunday as concerns over a rising number of cases of coronavirus threaten the Italian Grand Tour.

As Jhonatan Narvaez won stage 12 from a breakaway, a day intended as a celebration of Marco Pantani around his home town of Cesenatico became one of crisis for organisers as riders voiced their concerns and they were forced to address reports of an outbreak amongst police on the race.

EF Education First, winners of two stages in the opening 12 days, wrote to Giro organisers RCS Sport and the UCI calling for the race to end with Sunday's stage to Piancavallo – a request rejected by the world governing body.

EF manager Jonathan Vaughters said on social media the team's letter did not amount to a threat to leave the race but was a "suggestion that we feel is correct given the situation".

"We'd rather race all the way to finish in Milan. And if the next round of tests show it's safe to do that, we will," he added.

The team's letter, first reported by Eurosport, came two days after Mitchelton-Scott and Jumbo-Visma both withdrew their riders from the race following positives tests within their camps on the first rest day.

Mitchelton-Scott had already lost their team leader Simon Yates on Saturday following his own positive test for the virus.

EF's letter said: "With a clearly compromised bubble and an expected lag between exposure and symptoms/positives, it must be expected that further illness will result.

"This is not a given, but the precautionary principle would suggest we act responsibly and adopt a conservative approach."

Citing the possibility of further teams withdrawing individually, EF said ending on Sunday would be a "systematic, holistic way" to end the Giro "versus a chaotic withdrawal on a team-by-team basis".

EF said they would withdraw if any of their riders or staff tested positive in the days ahead.

However, the UCI rejected the request. In a letter signed by UCI president David Lappartient, the world governing body said Giro organisers RCS have "committed to implementing the measures to secure the race bubble".

The UCI later issued a statement in which it said RCS had agreed to undertake saliva antigenic tests on Thursday and Friday, before the next round of PCR tests are conducted as scheduled on Monday's second rest day.

"The organiser has also undertaken to implement measures to secure the race bubble, a central principle of the UCI protocol," the statement added. "The result of these measures will be closely monitored, and we will take any additional measures that prove necessary...

"Each of us must now take up the challenge of arriving in Milan on 25 October for the final stage of the Giro d'Italia and then finishing the remainder of the season, which can be achieved by continuing the spirit of collaboration and unity in professional cycling."

The day had begun with Lotto-Soudal's Thomas De Gendt telling Belgian broadcaster Sporza that he was unsure if the race should continue.

"I don't feel like riding today," the 33-year-old said. "The situation is headed in the wrong direction and it seems that the organisers are hiding things. The riders are discussing whether we should start the stage."

His comments came after reports that 17 police officers on the race had tested positive, though a police statement distributed by RCS said the individuals concerned had been working on the Giro-E, a support race.

The statement from RCS said that race has "completely separate" organisation, hotels and logistics, though there have been reports that some teams have found themselves sharing accommodation with those involved in the Giro-E event.

The RCS statement added: "As for the escort policemen on the Giro d'Italia, who follow autonomous prophylaxis dynamics, the recent Covid tests carried out have all returned negative responses."

On the road, Narvaez capitalised on a cruelly-timed mechanical problem for Bahrain-McLaren's Mark Padun to solo to victory out of the breakaway.

It was a third stage win of the race for the Ineos Grenadiers, delivered in cold and damp weather on the old stomping ground of 'Il Pirata' Pantani.

The overall contenders marked one another behind with a reduced bunch crossing the line a little over eight minutes after Narvaez to keep Joao Almeida in the pink jersey for another day, with his 30-second lead over Wilco Kelderman intact.

Domenico Pozzovivo and Vincenzo Nibali remain fourth and fifth respectively, while Narvaez's team-mate Tao Geoghegan Hart moved up to 12th overall, the best-placed Brit two minutes and 45 seconds behind Almeida in pink.