Two people are critically ill in hospital after suspected exposure to an "unknown substance" near the English town where a former Russian spy was poisoned with a nerve agent, officials said Wednesday.
Counter-terrorism police, who the led the investigation into the poisoning of Sergei Skripal and his daughter Yulia, said they were assisting local police in the investigation which has been declared a "major incident" by the emergency services.
Scientists at Britain's defence laboratory at Porton Down are carrying out tests to try and establish if there is any connection between the two incidents, British media reported.
The couple, a man and a woman in their 40s, were discovered unconscious at a house in a quiet, newly-built area in Amesbury, a village near the prehistoric monument of Stonehenge.
Local man Sam Hobson, 29, told AFP he was a friend of the pair, identifying them as Charlie Rowley and Dawn Sturgess.
He said that Sturgess fell ill first then Rowley later on.
"He was sweating loads, dribbling, and you couldn't speak to him, he was making funny noises and he was rocking backwards and forwards. It's like he was in another world," Hobson said.
Amesbury is about 12 kilometres (eight miles) from Salisbury, where the Skripals were found slumped on a bench in March in an incident that sparked a bitter diplomatic crisis with Russia.
PM 'regularly updated'
Prime Minister Theresa May's Downing Street office said the incident was being treated "with the utmost seriousness" and that she and top ministers were being kept "regularly updated".
Officials also held an emergency meeting at the Cabinet Office "to receive updates on the facts and the situation on the ground," May's spokesman said.
"The position we're at is as was set out by Wiltshire police overnight... it's important that we let them get on with their work."
The two patients "are both currently receiving treatment for suspected exposure to an unknown substance at Salisbury District Hospital," a police statement said.
"They are both in a critical condition."
The hospital is the same one where the Skripals were treated.
The pair were found on Saturday with police saying they initially suspected they had fallen ill after using "heroin or crack cocaine from a contaminated batch of drugs."
"However, further testing is now ongoing to establish the substance which led to these patients becoming ill and we are keeping an open mind."
'Such a quiet place'
Security cordons have been set up around the areas where the pair went before they fell ill with security boosted in both Amesbury and Salisbury.
A spokesman for Public Health England (PHE) said "it is not believed that there is a significant health risk to the wider public."
Local resident Natalie Smyth, 27, told AFP she saw fire engines and ambulances arrive at the house on Saturday.
"They shut the road. They said it was a chemical incident and then that it was drug-related.
"It is so strange, it is such a quiet place," she said, indicating that the emergency services personnel were wearing protective suits.
Robert Yuill, a local councillor, said the emergency services reaction to the incident was "far less intense" than after the Skripal poisoning.
Police 'containing any risk'
One of the areas cordoned off was Amesbury Baptist Church, where the pair had attended a party on Saturday.
"We understand this may well be the last event this couple went to in public," church secretary Roy Collins told reporters.
"We are all quite puzzled and shocked -- naturally the connection with Salisbury and recent events there mean there is a heightened public interest," he said.
Collins said around 200 people had attended the event but "nobody else has suffered any ill effects".
Wiltshire's Police and Crime Commissioner Angus Macpherson said there was "no reason to think it's connected" to the Skripal case.
Skripal, 67, and his 33-year-old daughter Yulia, who was visiting from Moscow, collapsed on March 4 in Salisbury and were treated for an extended period of time before being released from hospital.
A police officer who came to their aid, Nick Bailey, was also taken to hospital.
Moscow has rejected British accusations of involvement in the Skripal poisoning, which sparked a diplomatic crisis that saw Russia and the West expelling dozens of diplomats in tit-for-tat moves.
Britain said a Soviet-made nerve agent dubbed novichok was used on the Skripals.
