British police on Sunday sealed off part of Salisbury, where a Russian ex-spy and his daughter were poisoned by Novichok, after two people fell ill at a restaurant on Sunday following a "medical incident".
The local ambulance service said it was called to the scene and sent in ambulances and a hazardous area response team.
Roads were cordoned off around the Italian restaurant as police tried to determine what caused the pair to fall ill.
The two were said to be conscious.
"As a precautionary measure, the restaurant and surrounding roads have been cordoned off while officers attend the scene and establish the circumstances surrounding what has led them to fall ill," police said.
It was in the English city of Salisbury in March that Russian double agent Sergei Skripal and his daughter Yulia were poisoned with Novichok, a powerful nerve agent created in the Soviet Union.
Britain accuses Russia for that attack, a charge which Moscow has denied.
Skripal and his daughter survived the attack, but a British couple, Dawn Sturgess and Charlie Rowley, came into contact with the same nerve agent in a town near Salisbury months later. Sturgess, 44, died in hospital.
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