GPs may have to stop carrying out routine health checks in order to focus on the sickest patients as the coronavirus outbreak worsens.
The British Medical Association said routine monitoring of long-term conditions could stop, so GPs could "focus on the sickest patients".
There are also concerns about assessing patients, and supplies of protective equipment like gloves and masks.
NHS England said protective kits would be delivered to GPs this week.
Dr Richard Vautrey, chair of the BMA's GPs committee, warned patients with mild health complaints should expect to wait longer to see their GP.
"We do expect cases to rise rapidly and over the coming weeks," he told the BBC.
"We will need to stop doing much of the routine work that we do week-by-week to enable us to focus on the sickest patients and prioritise those who most need us.
"Practices that are routinely doing routine health checks, assessing blood pressure, diabetic control, and long term problems with heart and lung disease. Those routine checks will need to stop."
He added: "We'll need to prioritise not only those with potential Covid infections, but also the sickest patients who will need to continue to receive our direct care. It does mean that some patients may have to wait longer than normal to see their GP.
"It's likely to continue for at least a few weeks, if not months. And it's quite possible that there will be more than one wave of infection."
At the moment, there is guidance around testing patients who have been to a high-risk country in the past 14 days or have been in close contact with someone with coronavirus.
However there are concerns around patients who report a fever, cough and shortness of breath - the main coronavirus symptoms - but do not meet those criteria.
GPs said they were having to make difficult decisions about where to see patients, if they could not be managed on the phone, and there was a lack of guidance about what to do for them.
Some described measures such as seeing patients in a designated room or at the end of surgery. Others said they were wearing "catering aprons", due to a lack of equipment.
'No online booking'
Doctors also said they had contacted Public Health England (PHE) to find out more details of local diagnoses, but were unable to find out any more information than was already published online.
Two GPs, Dr Jane Wheatley and Dr Shivangi Thakore, both GPs in Islington, London, said they were only aware of a diagnosed case of Covid-19 in a parent of a local school in London when told by other patients.
The NHS 111 service had then asked a child at the school to come to the GP with symptoms of a cough and fever after a telephone triage.
It took three calls to Public Health England to decide what to do - and the child was eventually managed over the phone.
The GPs told the BBC: "We have struggled with deciphering and managing the seemingly conflicting information given by PHE and 111.
"It has incurred a heavy time cost, restricting our ability to practise; several GPs have had to dedicate time to strategic planning and lengthy phone calls to PHE, NHS 111, as well as local infectious diseases specialists."
Prof Martin Marshall, chair of the RCGP, said it was important that everyone in the NHS had "clear, concise guidance".
"GPs will increasingly be on the front line of dealing with Covid-19 - and we're already hearing from members that they are seeing more patients who are concerned about the outbreak and what steps they should take to protect themselves and their families."
He welcomed advice issued by the NHS to GPs last week, including the suggestion patients should no longer be able to book appointments online without being spoken to first.
But he added: "We are aware that there is some confusion around triage and the appropriate steps that GPs and their teams should take, particularly for patients who don't fit all current criteria for Covid-19.
"We are also aware of some concerns around community testing and the information on cases being made available to GPs. We are feeding this information back to NHSE and PHE."
An NHS spokeswoman said hundreds of protective kits would be sent out to GPs from this week.
These will include general use aprons, examination gloves and fluid repellent face masks.
Larger surgeries will receive repeat deliveries to ensure they have sufficient amounts.
"Almost all practices have no received protective equipment. As the supplies are used, more will be delivered," Mr Vautrey told the BBC.
A NHS spokeswoman added: "Anyone with concerns about coronavirus can use the NHS 111 online service, and while the 111 phone line is understandably busy, and people may have to wait longer than usual, all enquiries are being responded to, thanks to hard-working NHS staff."