Epsom Hospital was sealed off this morning due to an unexplained incident.
A concerned relative, who contacted the Epsom Guardian shortly before 10am, said patients were not being allowed in or out of the hospital.
Charles McManus said his wife Gilly and her father, 90, were among patients not allowed to leave the hospital without being told why.
Mr McManus said they went to the hospital at 9am and when they went to leave they were told they couldn't.
At 10am the security lockdown was lifted and the Epsom Guardian is still waiting for the trust to explain what happened.
People affected took to Twitter, as rumours spread that the lockdown could be caused by anything from a bomb scare to a baby being stolen.
Mrs Cakery tweeted "Husband is stuck in Epsom hospital- apparently a security lock down where no one can get in or go out. Bit like Willy Wonkas factory!!"
Sam Earls tweeted: "What us is happening at epsom hospital we are on lockdown?"
Mr McManus said rumours had started to fly among patients and visitors, adding: "They thought maybe a baby has been stolen which is why no one is allowed to leave the hospital.
"No one had got information and no one had been allowed to leave."
Before the patients were allowed out Mr McManus said there were fears the closure could last all day.
He said: "I’m a bit concerned really. I’m worried for my wife and how long this might go on.
"They are not really giving any information and that’s quite worrying."
The hospital trust has said a statement will be released within five minutes.
More to follow.
UPDATE: Anonymous threat leads to hospital lockdown