A ceremony on Wednesday for the two captains to unveil the series trophy was postponed to give Stokes time to recover.
“Several players and staff members, including England captain Ben Stokes, are feeling unwell and have been advised to stay at the hotel to rest up,” said the England and Wales Cricket Board in a statement.
Reports in British media said the players were suffering from viral food poisoning.
About half of the playing squad of 16 has been hit, according to the BBC, with only five taking part in an optional training session with around 14 members of the travelling party, including coaches and backup staff, advised to stay at the team hotel.
Joe Root, Zak Crawley, Harry Brook, Ollie Pope and Keaton Jennings were the players at training on Wednesday, while head coach Brendon McCullum was also in attendance. All of the squad had trained on Tuesday.
The virus outbreak could force England to change the team for the Test which had been announced on Tuesday.
Lancashire all-rounder Liam Livingstone is due to make his Test debut Thursday, while opener Ben Duckett was recalled for his first Test in six years.
England are on their first Test tour of Pakistan in 17 years, following their Twenty20 side playing seven matches in the country two months ago, taking the series 4-3.
Problems with food and players becoming ill during the Twenty20 series led to the decision to bring a chef, Omar Meziane, who also worked with the England men’s football team at the 2018 World Cup in Russia and at Euro 2020.
England and Pakistan will contest a three-Test series with the second in Multan beginning December 9 and the third in Karachi from December 17-21.
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