Two decades later, his daughter, Charlotte Harris Rees, read British author Gavin Menzies' 1421: The Year China Discovered the World, which posited that Chinese explorers had reached America years before Christopher Columbus.

Her interest piqued, Rees published an abridged version of her father's book, The Asiatic Fathers of America, and has since followed it with Secret Maps of the Ancient World. 'I was sceptical of my father's work at first, but then I started to think there was something to what he had said,' says Rees, who is a graduate of Columbia International University in South Carolina and now lives in Virginia.

'The information I have amassed on this subject is like a table with 100 legs. I have tried to use supporting 'legs' that are from academic studies and aren't easy to discredit. However, even if one were to knock off one or even a dozen legs on the table it would still stand because it has so much support.'

Some of Harris' extensive map collection has been dated to the Ming dynasty (1368-1644).

'The dating is partially done by looking at what is on the other maps in those books,' Rees says.

'Certain cities did not appear before certain dates, or cities changed names after certain dates. However, I remind everyone that my father always contended that his maps were not the original of this style of map, but came many years later and so were copies of copies of copies.'

Rees cites a number of examples to back up her latest theory. About 100 Peruvian place names are derived from Chinese, including the country's name, which is said to come from bai wu - loosely 'white mist' in Putonghua. A number of symbols associated with drawings by indigenous people in America are very similar to Chinese script. Native American infants share Asian babies' 'Mongolian spots' - a birthmark sometimes found near the base of the spine. And ancient Chinese villages bear comparison with Native American settlements, including the teepees.

'Remember, I entered this as a sceptic so it took a lot of 'supporting legs' before I, myself, believed this theory,' Rees says.

'I am a very patriotic American. My grandmother Harris was a member of the Daughters of the American Revolution. My goal is not to prove something for the Chinese but to arrive at truth.'

Reaction to Rees' theory has been enthusiastic, and Secret Maps has been endorsed by Dr Hwa-Wei Lee, retired chief of the Asian division of the Library of Congress, as well as by Menzies.

One persistent critic from Australia has tried to prevent Rees speaking about her theory both at Stanford University and the Library of Congress in the United States - attempts which were ignored by the authorities and left Rees puzzled.

The critic has not made it clear why he objects, but Rees takes it in stride. 'I realise that not everyone will agree with me - as the old saying goes 'none are so blind as those who do not wish to see.'

'Chinese discovering America certainly doesn't make the stock market go up or down or give someone back their job. It will not change the future of our country. However, so much of what we are told has a spin on it. I want to know the truth about our history.'

Rees says: 'Earlier last year I was invited to speak at the National Library of China in Beijing, but all speeches there were suddenly cancelled because of the threat posed by the H1N1 virus.

'I would love to see Hong Kong again. We lived in Sha Tin above the Buddhist temple garden. There was no road but many steps getting up to our place from the train station. When we first moved there boats were still sailing in the small harbour below - but I've heard that's since been filled in.'