Facing a crippling shortage of hospital beds and oxygen for Covid-19 patients as cases surge, India's capital city Delhi yesterday announced a week-long lockdown.

Delhi on Sunday recorded a high of 25,462 cases, putting already overloaded hospital and medical infrastructure under severe strain.

"I appeal to Delhiites to follow the lockdown, which is necessary to reduce Covid cases. We will improve the health system during this time," Delhi Chief Minister Arvind Kejriwal said, beseeching migrant workers not to leave the city. "If we don't impose a lockdown now, we might face a bigger calamity."

Only essential services are allowed to continue operating in the capital city. The announcement saw people make a last-minute dash to buy groceries and long queues at liquor vendors before restrictions came into force at 10pm.

With more than 15 million cases, India is the world's second-worst affected country after the United States, which has more than 30 million cases.

Covid-19 cases rocketed to 273,810 cases on Sunday, from some 100,000 in the first week of this month.

Former prime minister Manmohan Singh tested positive for Covid-19 yesterday, with Indian media reporting that he has been admitted to the All India Institute of Medical Sciences.

India saw a national 21-day lockdown last year, but this time, states are rolling out their own restrictions, depending on the situation on the ground.

Distress messages flooded Twitter, Facebook and WhatsApp as people appealed for blood, antibody-rich plasma from recovered coronavirus patients, and leads on available hospital beds, oxygen supplies and antiviral medication like remdesivir.

This time round, even well-connected people who would otherwise have no trouble getting help or navigating the system are appealing on social media.

Among those who turned to Twitter was Ms Richa Verma, whose brother, who was Covid-19 positive and in home quarantine, took a turn for the worse last Saturday evening.

Over four hours, Ms Verma called 25 hospitals and everyone she knew. Finally, in desperation, she reached out to The DeshBhakt, the social and political satire platform run by YouTuber and satirist Akash Banerjee.

A tweet from @TheDeshBhakt, which has 502,903 followers, helped her get two leads and hospital admission for her brother within minutes. He is now in stable condition.

"I called some of the heads of hospitals, medical directors, even political connections, ex-bureaucrats - whoever we could find. They all tried to arrange help. We were on the wait list for the next day or day after. We follow The DeshBhakt closely and we sent an SOS in case he could circulate it, and it worked," she said, noting that a Bharatiya Janata Party (BJP) worker also reached out to help.

"The entire community has come together and out to help complete strangers. Faceless people are tweeting or just forwarding messages of somebody asking for help," Ms Verma said, while noting there were people in India who did not have access to social media.

Even Minister of State for Road Transport and Highways V.K. Singh forwarded a tweet seeking help to get a bed for someone he said was like a brother in Ghaziabad in Uttar Pradesh.

He later said the person had been helped, but not without controversy over how even a government minister was turning to Twitter for help.

Political leaders and workers, cutting across political lines from the BJP to Congress, were also reaching out to help individuals and linking them up through their cadres with hospitals or pharmacies.

The worsening Covid-19 situation in India, with new strains emerging, also saw British Prime Minister Boris Johnson's planned visit next week cancelled.

He was scheduled to be in India on Sunday and Monday.

"In view of the prevailing Covid situation, it has been decided by mutual agreement that the Prime Minister of the United Kingdom will not visit India next week," said the Ministry of Affairs' official spokesman Arindam Bagchi.

He added that the two sides will be holding a virtual meeting in the coming days.