The World Health Organisation (WHO) said that the coronavirus originated in animals, but found it 'unlikely' that it was introduced to humans directly by bats.
It also said it was 'extremely unlikely' that the virus escaped from a Chinese lab.
Transmission could have also taken place beyond the wet market in Wuhan, central China, where the virus was thought to have emerged.
"The first cases were reported at the market. However, in other areas of Wuhan, transmission was also occurring," Liang Wannian, an expert with China’s Health Commission, said as the WHO's findings in Wuhan after a near month-long visit were announced.
Mr Liang said there was no substantial spread of the virus in Wuhan before the 2019 outbreak.
The WHO said that bats were not necessarily directly responsible for transmitting the virus to humans.
“All the work that has been done on the virus and trying to identify its origin continue to point towards a natural reservoir of the virus in bat populations," said Peter Karim Ben Embarek, programme manager at the WHO.
"But since Wuhan is not an environment for bats, the direct jump from a bat to the city of Wuhan is unlikely, so we have looked to see what other species could have introduced the virus in particular in the market."
Mr Liang said the coronavirus was circulating before the initial cases were reported in Wuhan.
The WHO also said that a laboratory being responsible for the virus' spread to humans was extremely unlikely.
There was no indication of coronavirus transmission before December 2019, the WHO said.
There is evidence of some spread at the seafood market in December but it’s “not the whole story,” said the WHO, which mapped the spread of the virus among earlier cases linked to the market and used genetic sequencing to identify the nature of the transmission.
“We know there was a spread of the virus among individuals who were not linked to the market so the picture is not clear… But the spread through frozen foods is not ruled out as some of the frozen wild animals are known reservoirs of Covid.”
While lab accidents do happen, they are extremely rare, Mr Embarek said. “We also looked at the Wuhan Institute of Virology and the state of that laboratory and it was very unlikely that anything could escape from such a place.”
"The findings suggest that the laboratory incident hypothesis is extremely unlikely in explaining the introduction of the virus into the human population, therefore, we do not suggest further work into that hypothesis for understanding the virus," Mr Embarek said.
Investigations showed that the virus was spreading beyond Wuhan and that these cases were missed.
"Based on research done on the virus from other studies around the world, the data suggests there was circulation preceding the initial cases and those cases that were missed were already circulating in other regions," Mr Liang said.
"We have also conducted research among 233 health institutions in Wuhan by searching records of those who had been sick based on their symptoms in the period of October 1 to December 10, 2019 and have reviewed the testing of blood obtained from the data banks and tested antibodies in blood samples," he said.
Around 50,000 samples from 30 species of wild animals have also been tested and all were negative, he added.