India is bracing for a third wave of coronavirus as its largest cities - the capital Delhi and financial hub Mumbai - see a surge in cases.

India reported 58,097 cases on Wednesday, a six-fold rise in a week that experts say is fuelled by the Omicron variant.

Nearly a third of those infections came from Delhi and Mumbai.

Both cities have brought back curfews and other restrictions to halt the spread of the virus.

Dr NK Arora, head of India's vaccine task force, told NDTV on Monday that the third wave of the pandemic had already begun in the country, adding that the "whole wave seems to be driven by a new variant... Omicron".

The country has reported more than 2,000 Omicron cases - Maharashtra, of which Mumbai is the capital, is leading the tally (653), followed by Delhi (464).

Delhi's health minister Satyendar Jain has said that 81% of Covid samples in the city tested positive for Omicron.

The All India Institute of Medical Sciences (AIIMS) - one of India's major hospitals - in Delhi has cancelled winter leave for doctors, according to reports.

Delhi was among the hardest hit cities as hospitals across the country ran out of beds and life-saving oxygen, leaving patients gasping for breath. Crematoriums were overwhelmed, forcing people to hold mass burials in open spaces.

Caseloads did drop eventually - for many months the national tally remained well under 10,000 cases a day.

Now as cases rise again, state governments are re-imposing restrictions.

On Tuesday, authorities in Delhi imposed a weekend curfew, with all non-essential activity banned between Friday night and Monday morning. The capital last week closed gyms and cinemas, as well as imposing an overnight curfew in an effort to stem the spread.

The weekend curfew decision was announced hours after the city's chief minister Arvind Kejriwal tested positive, saying he was isolating with mild symptoms.

Mr Kejriwal has been attending massive election rallies in other states, even as cases continue to rise in his city.

On Monday, he attended an event in Uttarakhand where many, including those sharing the stage with him, were seen without a mask.

Several other politicians, including Prime Minister Narendra Modi, have held similar rallies in Punjab and Uttar Pradesh in the past few weeks in which thousands - many without masks - have participated with little regard to social distancing.

The three states, along with Goa and Manipur, go to the polls in February and March.

Ahead of India's second wave too, political parties flouted Covid guidelines in states such as West Bengal where elections were due. The mega rallies were blamed for helping the virus spread.

But the Election Commission indicated last week that this year's polls may not be postponed even amid the rise in cases.

Meanwhile, authorities in Mumbai said they will consider imposing a lockdown if daily cases cross the 20,000 mark. The city recorded 10,860 new cases on Tuesday, a 34.37% jump from the previous day.

Cases are also rising in Goa, a tourist haven, where authorities have imposed a night curfew - it reported 592 new infections on Monday.

Goa saw massive gatherings and parties over Christmas and New Year's Eve, which experts say has contributed to the spike in infections.

India's government is yet to announce booster doses, although Mr Modi has said precaution doses will be given from 10 January to frontline workers and those above the age of 60 with comorbidities.

About 63% of India's eligible adults have been fully vaccinated and more than 90% have received at least one jab since the beginning of the vaccination drive in January 2021.

India has so far reported more than 34 million cases and 482,000 deaths from coronavirus, although experts say the true toll could be much higher.