CHENNAI (REUTERS) - India on Saturday (May 8) reported its highest ever single-day Covid-19 death toll, as cases continued to rise and states imposed stricter lockdowns.

India's health ministry reported 4,187 fatalities over the past 24 hours, taking the overall death toll to just under 240,000. Cases rose by 401,078, increasing the total since the start of the pandemic to 21.9 million.

Medical experts say the real numbers of Covid-19 cases and fatalities are likely to be far higher than official tallies.

Tamil Nadu, known for its automobile manufacturing including BMW, Daimler, Hyundai, Ford , Nissan and Renault, said it would move from a partial to a full lockdown on Monday, stopping public transport and shutting state-run alcohol retailers.

Neighbouring Karnataka state extended a total shutdown late on Friday. The state capital Bengaluru is a major tech hub, home to major offices of companies including Google, Amazon and Cisco.

India is yet to impose a national lockdown as it did during its first wave last year, but around half of all its states have imposed a total shutdown. The rest are under a partial shutdown.

Though it is the world's biggest vaccine maker, India is struggling to produce and distribute enough doses to stem the wave of Covid-19.

Although the country has administered over 167 million vaccine doses, its rate of inoculation has fallen sharply in recent days and only around 2 per cent of its 1.4 billion people have received the two doses needed to be fully immunised.

A crisis in the south

While cases in the country's northern and western areas have borne the brunt of the pandemic, southern states including Karnataka and Tamil Nadu have seen infections surge.

The second wave of the coronavirus pandemic in India has brought the healthcare system to the brink of collapse, with patients dying due to lack of oxygen or access to hospital beds.

Prime Minister Narendra Modi has been criticised for his handling of the oxygen shortage, though the government says it is doing all it can.

Tamil Nadu chief minister M.K. Stalin said in a letter to Mr Modi late on Friday Tamil Nadu's medical oxygen demand could double in the next two weeks.

"The availability of oxygen in Tamil Nadu is very very critical," Mr Stalin said, adding that 13 patients died in a hospital on the outskirts of Chennai due to the lack of oxygen.

Bangalore, which saw 1,907 coronavirus deaths in April, has recorded more than 950 deaths just in the first seven days of May. A lack of oxygen and critical care beds is being blamed for the dramatic rise in the death rate. The city of nine million people imposed its own restrictions on movement on April 25 but this has not stopped the grim statistics.

Coronavirus cases and deaths have also shot up in West Bengal state since its election, which was marked by huge rallies organised by Mr Modi and his arch-rival, state chief minister Mamata Banerjee. The main city, Kolkata, also has a critical shortage of oxygen and beds.

The country's top scientific adviser has warned of a possible third wave of infections.

"Phase 3 is inevitable, given the high levels of circulating virus," the government's principal scientific adviser, K. VijayRaghavan told a news briefing.

"But it is not clear on what time scale this phase 3 will occur... We should prepare for new waves."