GPs have been urged to be vigilant for severe strep A infections and to refer affected children to hospital immediately.
Doctors have been instructed by the government's UK Health Security Agency (UKHSA) to be particularly wary of invasive Group A streptococcal disease (iGAS) after a seventh child was reported to have died from the infection.
In the note sent by the UKHSA, GPs were told to set a "low threshold" for sending children potentially suffering from strep A to hospital and prescribing them antibiotics.
The number of cases of iGAS has risen this year, the UKHSA said, while there have also been "marked increases" in scarlet fever, which can be caused by strep A.
Strep A is a bacteria that is sometimes found in the throat or on the skin, and can be caught through close contact and from coughs and sneezes.
Usually, symptoms are mild such as a sore throat or a skin infection that may be treated with antibiotics, but it can cause scarlet fever, a disease that can come with a rash and a high temperature, sore throat and swollen neck glands.
Watch: UKHSA explains what strep A infection is and its symptoms
In very rare cases, strep A may get into the bloodstream and cause iGAS, which can be fatal. Symptoms include a high temperature of above 38C and severe muscle aches.
It has been reported that seven children have died in the UK since September from iGAS.
Last Friday, the UKHSA said six children under 10 had died after contracting a strep A infection in the past three months. On Saturday, it was reported that a 12-year-old boy from a school in south London had died after contracting the infection.
The UKHSA's alert has been sent to all GPs, A&Es and urgent care centres, and tells doctors to notify public health teams quickly about cases so contract tracing can be carried out.
In its note, the UKHSA says: “Given the unusually high level of GAS (Strep A) and viral co-circulation in the community, health care professionals are asked to have a low threshold to consider and empirically prescribe antibiotics to children presenting with features of GAS infection, including where secondary to viral respiratory illness."
It added: “GPs should maintain a low threshold for prompt referral to secondary care of any children presenting with persistent or worsening symptoms."
The UKHSA said there were 2.3 cases per 100,000 children aged 1 to 4 of iGAS this year, compared to an average of 0.5 in the pre-pandemic seasons (2017 to 2019).
There have been 1.1 cases per 100,000 children aged 5 to 9 this year compared to the pre-pandemic average of 0.3 (2017 to 2019) at the same time of the year.
Read more: What is Strep A and what are the symptoms?
In the week of 14 to 20 November, there were 851 cases of scarlet fever reported, compared to an average of 186 for the same period in previous years.
Among those to die from iGAS was seven-year-old Hanna Roap, from Penarth, Wales.
Her father, Hasan, 37, told the BBC she came home from school on 24 November with a cough, which became steadily worse.
She was prescribed steroids by a GP the next day but died later that evening.
Mr Road said: "My gut instinct is if she had antibiotics she would have been ok, but I'm not a medical professional, so I took what the GP said."
Four-year-old Muhammad Ibrahim Ali, from Buckinghamshire, died in an ambulance en route to hospital after contracting the invasive form of Strep A.
His mother, Shabana Kousar, told Sky News her son developed a red rash across his lower back and was prescribed antibiotics.
However, his symptoms persisted and he developed stomach pains before dying on his way to hospital in High Wycombe. A post-mortem examination revealed he had strep A in his blood.
Ms Kousar said: "I believe parents should be made aware of the symptoms and act on it if their child is experiencing something similar."
Four-year-old Camila Rose Burns, from Bolton, Greater Manchester, is fighting for her life on a ventilator at Alder Hey children’s hospital in Liverpool after contracting strep A.
Her father, Dean Burns, told Sky News he is "praying for a miracle".
Watch: Strep A infections leaves four-year-old girl fighting for life in hospital