Around a fifth of bowel cancer patients diagnosed in A&E had "red flag" symptoms in the year leading up to diagnosis, research suggests.
With many patients visiting their doctor repeatedly in the 12 months prior to being told they had cancer, the study indicated potential missed opportunities to pick up the disease.
Experts from University College London and the London School of Hygiene and Tropical Medicine examined National Cancer Registry data that was linked to GP data for 1,606 patients across more than 200 GP practices.
The study showed that "red flag" symptoms - which can include a change in bowel habit or bleeding - were much more common in patients who were diagnosed in places other than A&E.
However, 17.5% of bowel cancer patients and 23% of those with rectal cancer who were diagnosed in an emergency also had these "red flag" symptoms.
Most patients - regardless of how they were diagnosed - had also visited their GP in the year up to being diagnosed for various reasons. The number of visits to doctors increased significantly in the run up to diagnosis.
Cristina Renzi, lead researcher, Cancer Research UK scientist at University College London, said: "We know that patients diagnosed with cancer after emergency presentations don't do as well as patients who are diagnosed by their doctor through non-emergency routes.
"This study shows that most patients - who are picked up through the emergency route - can be harder to diagnose as they often don't show typical bowel cancer symptoms.
"However, in most cases they visit their doctor for various reasons multiple times during the months leading up to their diagnosis, which could represent opportunities to diagnose the cancer earlier.
"It's important to find ways to ensure these patients can be diagnosed at an early stage. And this study highlights the need to support GPs and give them the tools to diagnose and refer patients promptly when they feel it's necessary."
Dr Julie Sharp, Cancer Research UK's head of patient information and health, said: "This research shows the difficulties in diagnosing patients who are not showing typical symptoms of bowel cancer.
"In some cases where people have been diagnosed after an emergency presentation, there may have been opportunities for people to be diagnosed earlier, and it's important to try to find better ways of picking up these patients and getting them referred appropriately."
The study, published in the British Journal of Cancer, looked at five years' worth of data in the run up to patients being diagnosed.
A second study in the same journal found a clear association between cancer symptom awareness and cancer survival.
The research showed that in regions of England where cancer survival is poorer, people have, on average, lower awareness of cancer symptoms.
On average, each additional cancer symptom recognised was associated with about a 1.6% increase in one-year overall cancer survival for patients in that area.
East London had the lowest awareness of cancer symptoms while some of the highest were in Peterborough, Bedfordshire and Cambridgeshire.
Dr Maja Niksic, lead author of the study from the London School of Hygiene and Tropical Medicine, said: "A range of things can influence cancer survival. Stage of disease at diagnosis is one of them, and if we can ensure more people know what to look out for and see their GP if they notice any unusual or persistent changes, we may be able to reduce the numbers of patients who are diagnosed with advanced disease, where curative treatment is not often an option.
"Based on our research we think that health campaigns should focus on helping people to recognise cancer symptoms early and seek medical advice about these - especially in socio-economically deprived areas, where cancer survival is generally lower."