A blood test that can detect more than 50 types of cancer before any clinical signs or symptom of the disease has been developed by scientists.

The test is based on a type of DNA that is shed by tumours into the bloodstream known as cell-free DNA (cfDNA).

The researchers, including scientists from The Francis Crick Institute and University College London, said this method can not only tell whether someone has cancer, but also the type of cancer they have.

They believe the findings, published in the journal Annals of Oncology could in future help in the early diagnosis and treatment of tumours.

But experts say more work is needed to improve the test.

Commenting on the research, Dr David Crosby, head of early detection at Cancer Research UK, who was not involved in the study, said: "Although this test is still at an early stage of development, the initial results are encouraging.

"And if the test can be fine-tuned to be more efficient at catching cancers in their earliest stages, it could become a tool for early detection.

"But more research is needed to improve the test's ability to catch early cancers and we still need to explore how it might work in a real cancer screening scenario."

The test uses machine learning algorithms to look for chemical changes, called methylation, in cfDNA, which can contribute to tumour growth.

The researchers used the method on 4,316 samples - some with and some without cancer.

More than 50 types of cancer, such as pancreatic, lung and ovarian, were included in the study.

The test was able to predict the tissue in which the cancer originated in 96% of samples, and it was accurate in 93%, the researchers said.

Dr Michael Seiden, president of US Oncology in Texas, and senior author on the study, said the results showed that "targeted methylation" could be used for screening at population level.

He added: "Considering the burden of cancer in our society, it is important that we continue to explore the possibility that this test might intercept cancers at an earlier stage and, by extension, potentially reduce deaths from cancers for which screening is either not available or has poor adherence."

The study was funded by US-based company Grail Inc, maker of the blood test.