"John Lee (Augustyn) and Ben (Swift) both pulled out today because they literally could not continue as they were so sick," team principal Dave Brailsford told Reuters.
"Another three, Simon Gerrans, Ian Stannard and Pete Kennaugh are all really bad, how Simon and Pete got through today I just don't know, they were suffering so much."
Two sports directors and other members of staff have also been affected by the illness, which first hit the team on late Saturday.
"It's basically they can't stop vomiting but we don't think it's food poisoning," Brailsford said,
"We've got our own chef and the riders and staff eat separately and we're always very vigilant about hygiene"
Sky's top rider, Lars Petter Nordhaug of Norway is 34th overall but Brailsford said their main was about the health of the riders rather than the race itself.
"Right now we want to try and keep the team afloat. Then we'll see what happens."