Thousands of doctors across India wore black armbands on Tuesday calling for the arrest of a hugely popular guru who has claimed yoga can prevent Covid-19 and that conventional medicine has killed thousands of coronavirus patients.

Baba Ramdev, the creator of a successful traditional medicine empire, said last month the pandemic showed modern pharmaceuticals to be "stupid and failed science" and claimed hundreds of thousands "have died because they had allopathy (conventional) medicines".

On Tuesday's "Black Day" of protests, photos on social media showed doctors with banners demanding the arrest of "Quack Ramdev" while others wore PPE suits with #ArrestRamdev written on the back. 

The doctors' association at the All India Institute of Medical Sciences (AIIMS), one of Delhi's biggest government hospitals, called Ramdev's comments "disgraceful".

Ramdev, a keen supporter of Prime Minister Narendra Modi, retracted his comments after an appeal by India's health minister and the guru said he had been merely reading out other people's WhatsApp messages.

But he then caused further outcry by saying that he did not need a coronavirus vaccine because he was protected by yoga and traditional medicine, or Ayurveda.

Ramdev's company Patanjali Ayurved is worth several hundred million dollars, selling everything from toothpaste to jeans at its ubiquitous stores.

Earlier this year it launched a herbal remedy called Coronil that Ramdev, who also has a TV channel, had said would cure coronavirus. The launch event was attended by the health minister.

The company -- India's 13th most trusted brand according to rankings published last year -- has previously claimed it had cancer remedies, while Ramdev has also said he can "cure" homosexuality and AIDS. 

Coronavirus has left at least 330,000 people dead in India, including more than 1,200 doctors, according to the Indian Medical Association.