Emergency responders locking down a restaurant in the English city of Salisbury Sunday (September 17) after two people fell ill.

It's the same city where a poison attack shocked the country earlier this year.

In March, former Russian agent Sergei Skripal was poisoned along with his daughter Yulia.

Police say so far there's nothing to suggest Sunday's incident involved Novichok, the military-grade nerve agent used to poison the Skripals.

One of the sick people is said to be Russian - according to Sky News sources.

Police say the two fell ill while eating at Italian restaurant chain Prezzo, but added it's still unclear whether a crime has been committed.

Surrounding roads have been cordoned off as a precautionary measure.

Sergei and Yulia Skripal survived the attempt on their lives earlier this year but an unconnected woman - Dawn Sturgess - died in July.

She and her partner Charlie Rowley fell ill when they found a perfume bottle containing Novichok.

Earlier this month, Britain charged two men with the attempted murder of the Skripals, accusing the suspects of being military intelligence officers.

They also said the men were 'almost certainly' acting on orders from high up in the Russian state.

Two Russians resembling the men appeared on Russian television last week, insisting they were only tourists, visiting Salisbury for its cathedral.