Although processed meats have been classed in the highest risk category, alongside smoking, it does not mean that each are an equal danger, experts stressed.
The classifications describe the strength of the scientific evidence that a substance causes cancer, rather than the level of risk attached to it.
Dr Kurt Straif, from the France-based International Agency for Research on Cancer, said: "For an individual, the risk of developing colorectal (bowel) cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed."
Red meat - under which the IARC includes beef, lamb and pork - was classified as a "probable" carcinogen in its group 2A list that also contains glyphosate, the active ingredient in many weedkillers.
The lower classification for fresh red meat reflected "limited evidence" that it causes cancer. The IARC found links mainly with bowel cancer, but also observed associations with pancreatic and prostate cancer.
The World Cancer Research Fund (WCRF) has previously warned of "strong evidence" that consuming a lot of red meat can cause bowel cancer.
In 2009, it recommended eating no more than 2.5oz (70g) processed meat a week - the equivalent of three rashers of bacon - and said children should not have processed meat at all.
Industry tries to discredit report
New Zealand is in the top ten of countires for meat consumption. Before the report's publication the New Zealand meat industry was trying to discredit the findings.
Beef and Lamb New Zealand, which represents farmers and meat processors and retailers, said: ""There is no evidence to show any single food causes cancer,"
The lobby group's spokeswoman Fiona Greig said New Zealanders ate on average 22g of processed meat a day. "The causes of cancer are many and complex with lifestyle factors playing a key role in reducing cancer risk including maintaining a [healthy] body weight, not smoking and avoiding high intakes of alcohol," she said.
"Processed meat contributes nutrients to the diets of Kiwis and eliminating it completely is unnecessary. It can be enjoyed in moderate portions with plenty of vegetables and as part of an active, healthy lifestyle."
The Cancer Society's current advice states that red meats, including beef, lamb and pork, are "a valuable source of a number of different nutrients especially protein, iron, zinc and vitamin B12".
"It is recommended that people who eat red meat consume less than 500g a week, with very little, if any, processed meat. It is also recommended that care is taken when preparing and cooking red meat to avoid excessive fat intake and eating charred or burnt meat."
Professor Tim Key, from Cancer Research UK, said the links were backed by substantial evidence. He said the ruling should not mean cutting out all meats. "If you eat lots of it you may want to think about cutting down. You could try having fish for your dinner rather than sausages, or choosing to have a bean salad for lunch over a BLT.
"Eating a bacon bap every once in a while isn't going to do much harm - having a healthy diet is all about moderation," he said.
The new advice from WHO suggests 50g of processed meat is enough to significantly raise bowel cancer risk, by 18 per cent.
A fry-up including two rashers of bacon and two sausages makes up almost three times that amount, at 130g.
Dr Ian Johnson, nutrition researcher and Emeritus Fellow, Institute of Food Research, said: "Meat consumption is probably one of many factors contributing to the high rates of bowel cancer seen in America, Western Europe and Australia, but the mechanism is poorly understood, and the effect is much smaller than, for example, that of cigarette smoking on the risk of lung cancer. It is also worth noting that there is little or no evidence that vegetarians in the UK have a lower risk of bowel cancer than meat-eaters."
Speaking before the report was published, he pointed out that cigarette smoking increases the risk of lung cancer around 20 fold.
Q&A on meat and cancer
Q: Is bacon as dangerous as smoking?
A: No. The new report from the World Health Organisation has given processed meats such as bacon, ham and sausages, the highest ranking - "carcinogenic to humans".
Its inclusion as a group 1 carcinogen puts it alongside arsenic, alcohol, and asbestos as an agent which causes cancer.
However, the ranking does not compare the relative risks of the substances.
The classifications describe the strength of the scientific evidence that a substance causes cancer - not the actual level of risk.
WHO's team ruled that there processed meats do increase the risk of cancer, putting it in the top ranking. By contrast, fresh meat was assessed to be a "probable" risk - one rank down - as the evidence was less definite.
Q: How much does processed meat increase the risk of cancer?
A: The review found that every 50g of processed meat per day increases the risk of bowel cancer by 18 per cent, with increased risks of prostate and pancreatic cancer.
Q: How about fresh meat?
A: Studies in the review found that eating 100g a day of fresh red meat was associated with a 17 per cent increased risk of cancer, but that the evidence to support this was more limited, so that it was ranked as a "probable" cause of cancer.
Q: How do the risks of smoking and processed meat compare?
A: In total, 19 per cent of all cancers are caused by smoking, including almost nine in 10 lung cancers. Meanwhile, just 3 per cent of cancers are caused by processed and red meat - including around one in five cases of bowel cancer.
Q: Why does processed meat increase the risk of cancer?
A: Processed meat has been modified to change the taste or extend its shelf life. The main methods are smoking, curing, or adding salt or preservatives. Research has found that the compound that gives red meat its colour, haem, may damage the lining of the bowel.
Suspected carcinogenic chemicals can also form during processing. These include N-nitroso compounds and polycyclic aromatic hydrocarbons.
Q: Which products are defined as processed meats?
A: Simply putting beef through a mincer does not mean the resulting mince is "processed" unless it is modified further. Processed meat includes bacon, sausages, hot dogs, salami, corned beef, beef jerky and ham as well as canned meat and meat-based sauces.
The debate about processed meat and cancer
The links between processed meat and cancer have been debated for some time.
Why are they being linked?
One possible reason for the link is that the compound that gives red meat its colour, haem, may damage the lining of the bowel.
In addition, when meat is preserved by smoking, curing or salting, or by adding preservatives, cancer-causing substances (carcinogens) can be formed.
Studies have also found that people who eat a lot of red meat tend to eat fewer plant-based foods that protect against cancer.
What is defined as red meat?
Foods such as hamburgers, minced beef, pork chops and roast lamb are also regarded as red meat. As a rough guide, the WCRF says 500g of cooked red meat is the same as 700g of raw red meat.
What is defined as processed meat?
Processed meat is meat which has been preserved by smoking, curing or salting, or by the addition of preservatives. Examples include ham, bacon, pastrami and salami, as well as hot dogs and some sausages.
