The head of the World Health Organization (WHO) says further investigation is needed to conclusively rule out a theory that Covid-19 emerged from a laboratory in China.

Tedros Adhanom Ghebreyesus said on Tuesday that although a laboratory leak is the least likely cause, more extensive research is needed.

The virus was first detected in Wuhan, in China's Hubei province in late 2019.

The Chinese government has dismissed the allegations of a virus leak.

Since the novel coronavirus was first identified, more than 2.7 million people are known have died from it, with more than 127 million cases worldwide.

An international team of experts travelled to Wuhan in January to probe the origins of the virus. Their research relied on samples and evidence provided by Chinese officials.

Dr Tedros said the team had difficulty accessing raw data and called for "more timely and comprehensive data sharing" in the future.

The team investigated all possibilities, including one theory that the virus had originated at the Wuhan Institute of Virology. The institute is the world's leading authority on the collection, storage and study of bat coronaviruses.

Former US President Donald Trump was among those who supported the theory that the virus might have escaped from a lab.