The man in his 40s who collapsed at a restaurant in Salisbury with his female dinner guest was said to be in a critical but stable condition today.
A major incident was declared yesterday when the man, who is believed to be Russian, and a woman in her 30s became unwell at a Prezzo restaurant in the city.
Roads were cordoned off and police and paramedics wearing protective suits were deployed amid heightened tensions following the deadly Novichok attack.
Today police officers were standing outside the Prezzo, which remained closed, and staff were being allowed in. It remains unclear when it will re-open for business.
But fears the duo had become the latest Novichok victims were allayed after police said there was nothing to suggest the nerve agent had caused them to fall ill.
Offices closed Prezzo and nearby roads after the 'medical incident' at 5.30pm near to where ex-Russian spy Sergei Skripal and his daughter Yulia were poisoned.
Witnesses described police 'covering someone up with a blanket', and claimed the victims were Russian. Police took diners to an empty shop after the incident.
Amanda Worne, who was at Prezzo, tweeted: 'Salisbury leaps into action again as two Russians are taken ill in Prezzos showing the same symptoms as before. We were next to them.'
Sam Proudfoot, 16, tweeted: 'Trouble in Salisbury again near the cathedral. There's a man in a full white body suit with a mouth-mask.'
Another witness told the BBC that one of the people taken ill was a blonde woman in her late twenties.
The female appeared to be at the table on her own and 'kept going away and coming back'. The witness added: 'When she came back she was hysterical.
'She called paramedics and the next thing an ambulance turns up and they come rushing in.'
Novichok's deadly effect on Salisbury
Sergie and Julia Skripal were poisoned in March after Novichok was smeared on Mr Skripal's front door in Salisbury. Police officer Nick Bailey was also treated after being contaminated.
Almost four months later, locals Dawn Sturgess and her partner Charlie Rowley were taken to hospital after handling a discarded perfume bottle used to carry the nerve agent.
Miss Sturgess died and Mr Rowley remains in hospital fighting meningitis after the poison weakened his body.
The incident comes days after two suspected Russian spies appeared on pro-Kremlin TV to deny being behind the attack on the Skripals.
Alexander Petrov and Ruslan Boshirov said they were in Salisbury to visit the cathedral after CCTV showed them close to Mr Skripal's home.
But traces of Novichok were found in their hotel room. Their incompetence is said to have angered Vladimir Putin, and they are thought to have been put before TV cameras as punishment.
The source added that the man the woman had been with had gone to the toilet and had had a fit.
Amanda Newton, who was in the restaurant, posted on Facebook: 'Two people sitting next to us taken seriously ill and the whole area is closed. We may need blood tests at hospital.'
Phil Downton, a member of staff at the nearby New Inn said that the diners were brought to the pub until the all-clear was given at about 1am.
He said: 'We weren't allowed to go near them, they were on one side of the pub and we were told not to go in there just in case of contamination if it was something.'
A business owner five doors away from the Prezzo said her company had suffered significant losses since the first Novichok attack in March this year.
Sarah Orton, owner of Roly's Fudge Pantry, said her company are £25,000 worse off than they were this time last year and last night's episode was an overreaction on the part of emergency services.
The 54-year-old said: 'They should have dealt with it quietly but instead there were multiple police cars and ambulances, it just makes the whole incident seem worse than it is.
'The police are overreacting and it's having a huge effect on the city and the businesses here, it's giving Salisbury a very bad reputation.
'It is so unfair on all of us business owners. As a company we had two really successful years then since the first Novichok attack it has been dead.
'I offer my sympathies to those who were taken to hospital unwell last night, but it is absolutely ridiculous to think it is a Novichok attack every time someone falls ill.
'They could be having a heart attack, or a seizure, but from now on this is what it will be like.
'I don't understand why people think it isn't safe, Novichok doesn't just linger in the air, it has to be planted by people.
'It's had a huge effect on my business as well as others, we are £25,000 worse off than this time a year ago.
'I think everyone in the city is just fed up with it now - how much longer is it really going to carry on?
'There are still so many questions that haven't been answered and the local people deserve to know what's going on.'
However, bus driver Darren Cottrell said the last six months has 'put Salisbury back on the map'.
Speaking from outside the Prezzo restaurant, he said: 'It's not right that people who live here have to wait for the news each night to know what's going on.
'The only positive about this whole situation is that it has put Salisbury back on the map.
'Maybe one day people will visit the city because of this whole incident, it could almost be some sort of tourist attraction.
'We just want answers now, we've had parts of our city cordoned off all over the place, but no one is ever explaining to us what's going on.
'Everyone knows this is what it's going to be like for years now. People are worried and panicking and they will jump to conclusions whenever anyone is unwell.'
Wiltshire Police said last night they did not believe the two victims were exposed to Novichok.
A spokesman added: 'Due to recent events in the city and concerns that the pair had been exposed to an unknown substance, a highly precautionary approach was taken. Both were taken to hospital and assessed.
'We can confirm that there is nothing to suggest Novichok is the substance. Both remain in hospital under observation.'
The Italian restaurant is a short walk from Queen Elizabeth Gardens, which was until recently closed off after Dawn Sturgess was fatally poisoned by Novichok in June.
Also nearby is Zizzi, the Italian restaurant where former spy Sergei Skripal and his daughter Yulia visited before they were taken ill in March.
Police said 44-year-old Ms Sturgess was killed by the same chemical used in an alleged hit by Russian military intelligence officers on Mr Skripal.
Salisbury City Council leader Matthew Dean tweeted: 'Rightly the emergency services start with a highly precautionary approach until they know otherwise.'
Salisbury District Hospital remained open during the incident. Cara Charles-Barks, chief executive of Salisbury NHS Foundation Trust, said staff did an 'amazing job'.