A spate of deaths has rocked the homeless community in Oxford, sparking warnings that a lack of housing and support for people with mental health and addiction problems in one of Britain’s most affluent cities is contributing to fatalities.

Bereaved friends of three men and a woman who have died suddenly in the university city since November said the losses are the worst they have known. They fear further deaths among rough sleepers amid freezing temperatures.

The latest came on 21 January when Sharron Maasz, 44, a drug-addicted mother and grandmother, died in an intermediate home after a long period sleeping rough and a spell in hospital.

The deaths have deeply upset Oxford’s growing community of rough sleepers, many of whom claimed this week that highly vulnerable people are being left with insufficient support even when they are given beds.

On 2 December Aron Gibson, 37, died in the McDonald’s on Cornmarket Street, the main shopping street, on a Sunday evening, reportedly when an attempt to inject drugs into his groin went wrong. Four days later a Polish gardener, Czeslaw Mazak, 36, who slept rough and often without a tent, was found dead near a city centre nightclub on 6 December. A friend said he was “proud” and had refused offers of shelter. Simon, a man in his 50s, died shortly after moving from the city’s main homeless hostel into shared housing, friends said.

“I knew Sharon, Simon, Chester [as Czeslaw was known locally] and Aron,” said Tom Cash, 53, a Big Issue seller. “It hurts me. Aron was buried and no one knew it. It was like he was John Doe. I would have liked to have gone.”

Monica Gregory, a formerly homeless woman who volunteers to support rough sleepers in her city, said: “I am worried about who is going to be next. This is the worst I have seen it in Oxford.”

The spate of deaths emerged on the eve of the government’s latest annual count of rough sleepers in England and Wales, which rose 15% to 4,751 rough sleepers in 2017. Councils and homeless campaigners are expecting it to rise again. A total of 597 people sleeping rough or in emergency accommodation were estimated to have died last year in England and Wales, a 24% increase from 2013.

In 2017 Oxford recorded the highest average house prices in the country compared with local earnings, but the city’s 56-bed main homeless hostel is full and up to 35 people also sleep on the floor on the coldest nights. Five tents are pitched a few yards from its front door. Another 61-room hostel was demolished this year to make way for conventional housing.

“These deaths impact everyone,” said the Oxford city councillor Shaista Aziz. “Homelessness is a national humanitarian emergency and we are seeing its daily implications in our city.”

Estimated rough sleeping per capita is higher in England only in Brighton, Bedford, Luton, Westminster and Camden and has risen more than tenfold since 2011 from eight to 89 in 2018.

Aron was buried and no one knew it. It was like he was John Doe. I would have liked to have gone Tom Cash, Big Issue seller

Linda Smith, the deputy leader of Oxford city council, said: “Every death of a rough sleeper is a death too many … Homelessness kills and the best way to help a rough sleeper is to get them to come inside where they can get the accommodation and support they need to rebuild their lives away from the streets.”

However, Maasz died in interim housing funded through the council.

Wrapped in blankets two doors along from the McDonald’s where Gibson died, Kaz, 61, broke down when she remembered her “best mate” Sharron.

“There was no need for it,” she said. “She shouldn’t have been left alone. All the girls need support, all the lads too.”

On Wednesday, Oxford’s senior coroner, Darren Salter, opened an inquest into Maasz’s death. He said she died in her accommodation on Botley Road in west Oxford and pending toxicology, items at the scene suggest her death was drug-related.

Kaz (right) cries as as she is comforted by Monica Gregory (left) and Jackie Keating as she remembers her homeless friend Sharron Maasz who died on the streets of Oxford. Photograph: Andy Hall/The Observer

Only five months ago Maasz told the Guardian: “I just want to get my life sorted. I want to put a lid on all the chaos. I’ve always wanted to get clean, but it’s not as simple as that if you’ve got mental health issues and you’re living like this, being pushed from pillar to post.”

After that she was in hospital for about eight weeks with an infection caused by needle use which required an operation.

“She could hardly walk,” said Gregory. “She used to ride a bike to keep the pressure off her leg. She fought and fought to get into a hostel. Three weeks before she passed away she got put into the women-only project. I feel disgusted. She should have had help.”

Jackie Keating, 54, a former cleaner from Leeds who has been homeless in Oxford for nine months, said she had twice almost died on the streets from pneumonia and from a thrombosis in her leg which burst causing an open sore like a bullet wound that became infected. She was also beaten up twice.

“Sharron’s death hit us hard,” she said. “She was a good woman.”

“It is a stark reality that particularly over winter, people are going to lose their lives,” said Claire Dowan, the chief executive of Homeless Oxfordshire, which had housed Maasz and Gibson and runs the O’Hanlon House hostel. “We are saving lives but we are at crisis point here. We are full to the gills.”

She said that when visitors see the floor of the communal areas full of people sleeping on the floor, they remark that it seems as if a natural disaster has happened.

“Our staff know that from time to time there will be deaths,” she said. “We expect it but we don’t accept that’s the way things should be.”

• This article was amended on 31 January 2019 to remove references to the death of Otis Galloway in a house run by Homeless Oxfordshire. After publication, the Guardian was notified that the information provided by local officials was inaccurate and Mr Galloway was not placed there due to homelessness.