The Union Health Secretary wrote to the Maharashtra, Kerala, Chhattisgarh and Bengal governments on Thursday to underline the need for "strict vigil" and "prompt action" to arrest the recent spike in coronavirus cases in each of the states. These four states account for 59 per cent of all active Covid cases in the country, the Health Secretary, Rajesh Bhushan, said in his letter.

The state governments were also warned against allowing testing rates to drop - particularly in light of the spread of a mutated (and considerably more infectious) strain of the virus - and to aggressively implement the 'Test-Track-Treat' strategy deployed by other states.

Mr Bhushan also reminded state authorities to urge people to wear face masks, maintain social distancing and follow all other Covid-appropriate behaviour.

The letter comes after Health Minister Dr Harsh Vardhan singled out three of the above four states - Kerala, Chhattisgarh and Maharashtra - and said a surge in cases served as a warning that the war against the novel coronavirus is far from over despite the presence of multiple vaccines.

"Maharashtra, Kerala and Chhattisgarh have seen a sudden spike in coronavirus cases recently. This gives us a warning that we shouldn't forget precautions and (must) continue our fight against COVID-19," Dr Harsh Vardhan told news agency ANI earlier today.

Maharashtra remains the worst-affected state with around 52,000 active cases and nearly 50,000 deaths linked to the virus. Chhattisgarh and Bengal have around 9,000 active cases each; Bengal has reported nearly 10,000 deaths while Chhattisgarh has recorded around 3,500 so far.

Kerala has seen an average of over 5,000 new cases per day in the past week. Maharashtra has seen over 3,700 in the same period, while Chhattisgarh saw an average of 1,006 and Bengal 908.

Kerala has also seen a worrying surge in infections, with active cases shooting up past 65,000 this morning. On Monday the southern state also reported its first case of the UK strain of the virus - six have been detected so far.

Across India more than 70 cases of the new strain have been reported so far. Overall India has 2,29 lakh active cases and has reported over 1.5 lakh deaths since the pandemic began in December 2019.

Dr Vardhan has said the government is in the final stages of vaccine roll-out and that around 30 crore people will be injected in the first phase. The government has already conducted one national dry run to proof the vaccine delivery system and a second will be held Friday.