Britain must now prepare itself for more cases of the coronavirus, health officials have warned, as they confirmed a first victim diagnosed in London on a day when the spread of the disease continued to cause disruption across the world.

The new patient, who brings the total number in the UK to nine, is a Chinese woman in her late 20s or early 30s who lives in the British capital with relatives. She flew in to Heathrow from China at the weekend and called NHS 111 when she developed symptoms after landing.

She was tested at a London hospital on Sunday afternoon, returned to her London home and kept herself in isolation there. It is not known if the family members she lives with have been tested.

Officials have been ordered to trace relatives, friends and anyone she may have been in contact with since returning to London in an attempt to slow the spread of the virus. Fellow passengers on her flight will be contacted and offered testing too.

As schools in Brighton, where two GP surgeries have already closed because of the outbreak, instructed pupils to self-isolate, there were warnings that the public should be prepared for the coronavirus – now named Covid-19 – to spread further.

Dr Paul Cosford of Public Health England said that more cases were now highly likely and that a growing number of people travelling into British airports could be infected.

As PHE sought to ascertain the significance of the new case, a growing number of public events around the world were being cancelled in an attempt to slow the spread of the virus, which can lead to pneumonia and has so far killed more than 1,100 people in China alone.

On a day of fast-moving developments:

• A major technology trade fair, the MWC in Barcelona with 100,000 attendees due to begin next week, was cancelled, as was April’s Chinese Grand Prix.

• A cruise ship that was turned away from five countries was finally allowed to dock in Cambodia.

• Cases fell to their lowest in weeks in Hubei province – but experts urged caution over claims that the fight against the virus was being won.

• An additional 39 people on board the Diamond Princess cruise ship tested positive, plus one local official who contracted the virus while on board.

• At Arrowe Park Hospital in Merseyside 83 people in quarantine were told they would be allowed to leave on Thursday after they all tested negative, while the Guardian understands that all those quarantined in Milton Keynes since Sunday have also tested negative.

Health bosses speculate that the virus will continue to spread in the UK until it peaks in the summer, later than the previous assumption that it would peter out in the late spring. A source said: “We are planning that we are into this for the next few months.”

Other experts said it was too soon to tell whether the new case implied that the virus would spread in the capital, a key transport hub with a population of nine million.

“It is really not surprising that a case has been reported from London,” said Jon Cohen, emeritus professor of infectious diseases at Brighton & Sussex Medical School. “We will not really be able to estimate the potential risk of onward spread until further information on this patient is known, including details of how long they were in the UK until they were diagnosed and what their movements were.”

Dr Michael Head, senior research fellow in global health at the University of Southampton, said evidence for the role played by public transport like the London Underground in the spread of a virus was “fairly limited”, adding that long-distance trains and international travel were likely to be more important factors.

He noted that of the 1,750 tests carried out so far in the UK, more than 99% had been negative.

Dr Robin Thompson, junior research fellow in mathematical epidemiology at Oxford University, said there were some risks associated with a diagnosis in London, but noted that if the patient had quickly self-isolated, then the danger could be mitigated.

“In general, if an initial case is in a densely populated area, then the risk of sustained person-to-person transmission following is higher,” he said. “This is exacerbated by the fact that London is a transport hub, and the underground could provide a network to spread the virus quickly.

“However, the key factor here is the number of contacts that this infected individual has had prior to being isolated. If this is low, then the risk of sustained human-to-human transmission is also low.”

In Brighton, the businessman who unknowingly contracted the virus and is suspected of being at the centre of a cluster of cases said he is “happy to be home” after being discharged from hospital. Steve Walsh was discharged from hospital on Wednesday and is no longer contagious, NHS England said. Officials are optimistic that no other cases will be linked to him.

“I want to give a big thank you to the NHS who have been great throughout and my thoughts are with everyone around the world who continues to be affected by the virus,” the 53-year-old scout leader said, adding that he was feeling well. “It’s good to be back with my family and I would ask you please to respect our privacy from this point on.”

At least nine schools in Brighton, Hove and Eastbourne in East Sussex informed families that some of their pupils or staff had been told to self-isolate after concerns were raised that Walsh, who tested positive for coronavirus, may have passed it on to others.

Walsh, who contracted the disease on a business trip in Singapore before going on a ski trip, where he is thought to have infected others, was being held in an isolation unit at St Thomas’ hospital in London. He was in the Alps with two GPs who have since tested positive for coronavirus in Brighton.

It was confirmed on Wednesday that 12 patients and medical staff who came into contact with doctors diagnosed with the coronavirus in Sussex had been traced.

The two GPs worked between Worthing hospital’s A&E department, a nursing home and two doctor’s surgeries in Brighton, Public Health England said. One of the infected GPs named locally as Dr Catriona Greenwood had worked as a locum doctor at the hospital. It also said that all those who came into doctor with the two doctors were now receiving medical advice.

Meanwhile, in Oxfordshire, tests on two prisoners at HMP Bullingdon provided negative results for coronavirus. The prisoners, one of whom had recently been transferred from a jail in Thailand, had been kept in isolation in their cells.