The UK now has at least 21 cases of monkeypox - with more expected to be announced later today.
Scotland has recorded its first case, with the other 20 detected in England.
Health officials are expected to give an updated UK total later, with the government warning that close contacts of cases with the highest risk of exposure should self-isolate for 21 days.
Monkeypox is spreading in the UK through community transmission and new infections are now being detected on a daily basis, a senior doctor has warned.
Officials are expecting a "significant rise" in infections this week, after the total increased to 20 on Friday.
Dr Susan Hopkins, a chief medical adviser from the UK Health Security Agency (UKHSA), told the BBC's Sunday Morning programme: "We are detecting more cases on a daily basis.
"We know there's been a period of restrictions across Europe, and we don't know where this infection has come from and how it's come into Europe.
"There's no obvious connection in our cases in the UK to a single event."
New guidance from the UKHSA recommends people who have had "unprotected direct contact or high-risk environmental contact" with the disease should isolate - and avoid contact with immunosuppressed people, pregnant women, and children under 12.
Those contacts include household contact, sexual contact, or changing an infected person's bedding without wearing appropriate PPE. They should also be offered a vaccine.
'Outbreak is a concern'
Globally, US President Joe Biden has said the outbreak is "a concern", while Israel and Switzerland recorded their first cases this weekend and Austria registered its first suspected infection on Sunday.
Following the COVID pandemic, the outbreak of an unusual disease has gripped people's attention in several countries.
Belgium has reportedly introduced a 21-day quarantine for those who contract monkeypox after four infections were recorded in the country.
The disease, which was first found in monkeys, can be transmitted from person to person through close physical contact - including sexual intercourse - and is caused by the monkeypox virus.
It causes fever, body aches, chills, and fatigue in most patients, while people with severe cases can develop a rash and lesions on the face, hands and other parts of the body.
'We don't know where this infection has come from'
Dr Hopkins said the illness is "relatively mild" in adults, with young children more at risk, but refused to comment on reports that a patient is being treated in intensive care.
She said the risk to the general population "remains extremely low at the moment" but people "need to be alert to it".
"We're saying to people if you've got symptoms, avoid close contact with others and seek medical attention," she added.
She said early symptoms are "non-specific" and feel "like a viral-type infection".
In later stages, people develop a rash, usually to the face, hands and arms, that can also affect genital areas.
"It starts as red spots and moves to vesicles - those are blister-type lesions that are a bit like chickenpox," Dr Hopkins said.
"They scab over and once the scabs have fallen off, they're no longer infectious."
The World Health Organisation held a live Q&A on Monday in which a panel of experts answered questions on the recent spike in monkeypox cases.
Dr Rosamund Lewis of the WHO Emergencies Programme, said monkeypox and COVID are different viruses that "spread in a different manner".
"The way it does spread is through close physical contact. People who have monkeypox develop a rash and that rash can be contagious."
The WHO experts said that scientists currently do not have an answer if the virus is mutating, but since it is a DNA virus, the mutation rate is much lower than for RNA viruses.
"So it's a very stable virus," Dr Lewis said. "We don't yet have evidence that there's a mutation in the virus itself."
The WHO said that anyone who comes into close physical contact with somebody with monkeypox is different to COVID in terms of how it is spread and that it is a "containable infection".
Elsewhere, Professor Paul Hunter at the Norwich School of Medicine at the University of East Anglia told Sky News: "We have actually seen an outbreak in this country in the past, in about I think it was 2018, where a small outbreak with a travel related case who then passed the infection on to healthcare workers.
"It is an infection that has been increasing globally for a few years now, and typically the outbreaks in the West have generally been associated with animal contact.
"But this is indeed the first time that we've seen such a large outbreak across multiple countries where there has been person to person transmission outside of Africa," the professor said.
"In adults, it is a usually a pretty mild infection that gets better on its own, typically within about three weeks, although sometimes you do get left with scarring," added Prof Hunter.
"But it can be severe, particularly in children and also in people who are immunosuppressed, and probably also in pregnant women," he said.