The Centre may ask states and union territories to take a call on future curbs on their respective jurisdictions after lockdown 4.0 ends on May 31.

However, the same will be outside a nationwide 'negative' list that is likely to continue to prohibit international flights and resumption of schools and colleges.

According to sources cited by the Times of India, the lockdown measures may be assessed every fortnight until restrictions are gradually phased out, in line with the developing situation.

The role of the central government will eventually be limited to announcing a step-wise and smaller list of barred activities nationally and defining national directives on COVID-19 management such as wearing masks compulsorily, as well as observing social distancing, the news report added.

The Union Ministry of Home Affairs came out with the last set of lockdown guidelines on May 17 that had left it to states to decide on delineation of red, green, and orange zones as well as taking a call on the degree of relaxations to the states/UTs.

The Centre had allowed everything except a select few barred activities such as re-opening of educations institutions, cinema halls, gyms, shopping mall, swimming pools, resumption of domestic and international passenger flights, public gatherings comprising religious assemblies.

Eventually, domestic passenger flights were resumed from May 25 but with specific rules and guidelines such as the mandatory wearing of face masks by passengers, cap on ticket pricing, no food service onboard flights, and furnishing details of medical conditions by travellers via the Aarogya Setu app or by filling up a self-declaration form.

India's top medical body, the ICMR has said human trials of coronavirus vaccine may begin in another six months.

Dr. Rajni Kant, Director Regional Medical Research Centre and Head at the Indian Council of Medical Research (ICMR) told news agency IANS that, "The virus strain isolated at the National Institute of Virology (NIV) laboratory in Pune will be used to develop the vaccine. It is expected that the human trials of the vaccine will begin in at least six months". Kant added that virus strain had been successfully transferred to the Bharat Biotech International Ltd. (BBIL).

Union Health Minister Harsh Vardhan, on Sunday, said that four out of the 14 COVID-19 vaccine candidates from India may enter the clinical trial stage in the next three-five months.

Vardhan added that industry, academic world were contributing to the clinical trial. Additionally, Ministry of Science was helping the Department of Biotechnology in all such efforts. The Department of Biotechnology has been made a central coordination agency to identify pathways for vaccine development in the  country.

Vardhan said, "It's very difficult to predict when a vaccine will come, but as a doctor, I can say that the process it involves, one year would be a modest estimate".

Meanwhile, US Biotech firm Novavax has also joined the list of companies to statrt human trials of a vaccine for the coronavirus disease.  

As of May 26, there were at least 10 vaccines in human trials, according to the World Health Organisation (WHO).

A Pakistan International Airlines flight from Lahore, with 91 passengers and eight crew on board, crashed near the Karachi airport, just a minute before the Airbus A320 was to land this afternoon. There are no reports on the number of casualties yet.

The PIA flight PK-8303 went down in what looks like a densely populated residential area - Jinnah Garden area near Model Colony in Malir - just short of the Jinnah International Airport. The crash comes just days after Pakistan began allowing commercial flights to resume after planes were grounded due to the lockdown over the coronavirus pandemic.

The wreckage and several houses in the area are on fire, visuals by Pakistan media showed. Plumes of smoke could be seen billowing in the sky as ambulances tried to make their way through.

25 residents of the area, injured in the crash, have been reportedly taken to hospitals. An emergency has been declared in all major hospitals of Karachi.

News agency PTI quoted sources in Pakistan's Civil Aviation Authority as saying that communication with the plane was cut off one minute before its landing.

Pakistan Prime Minister Imran Khan said and immediate inquiry will be instituted in the crash. "Shocked & saddened by the PIA crash. Am in touch with PIA CEO Arshad Malik, who has left for Karachi & with the rescue & relief teams on ground as this is the priority right now. Immediate inquiry will be instituted. Prayers & condolences go to families of the deceased," he tweeted.

Pakistan media reported that Pak Army Quick Reaction Force and Pakistan Rangers are at the crash site to assist in relief and rescue efforts, which have been hindered due to the presence of a large crowd and narrow lanes.

Karachi and Lahore are about 1,020 km apart and it takes under two hours for a flight to cover the distance.

In 2016, a Pakistan International Airlines plane burst into flames after one of its two turboprop engines failed while flying from the remote northern to Islamabad, killing more than 40 people.

Domestic passenger flights will resume from Monday "in a calibrated manner", the government said today. 

Flights were stopped in late-March, when the country went into lockdown to slow the spread of coronavirus.

"Domestic civil aviation operations will recommence in a calibrated manner from Monday 25th May 2020. All airports and air carriers are being informed to be ready for operations from 25th May," tweeted Civil Aviation Minister Hardeep Puri.

SOPs for passenger movement are also being separately issued by the ministry, he said.

Domestic civil aviation operations will recommence in a calibrated manner from Monday 25th May 2020.

All airports & air carriers are being informed to be ready for operations from 25th May.

SOPs for passenger movement are also being separately issued by @MoCA_GoI.

— Hardeep Singh Puri (@HardeepSPuri) May 20, 2020

Cargo flights, those for medical evacuation and special flights to repatriate Indians stranded abroad have been operating during the lockdown.

The government as well as airlines have talked about a "new normal" when flights start again, with fewer passengers in a flight, mandatory masks and the middle seat left vacant for physical distancing.

Earlier, when Prime Minister Narendra Modi had announced lockdown4 with incremental easing of restrictions, aviation regulator DGCA had asserted that scheduled commercial passenger flights would stay suspended till May 31.

Yesterday, the minister had tweeted that it was not upto the central government alone to decide on when domestic flights could restart.

"In the spirit of cooperative federalism, the government of states where these flights will take off and land should be ready to allow civil aviation operations," Hardeep Puri had tweeted on Tuesday.

Airlines have suffered huge losses since various countries stopped flights in their fight against the pandemic. India first blocked the entry of people from abroad and then stopped flights altogether as it went into total lockdown.

Yogi Adityanath asks all states for details of migrants, 12,000 buses to ferry Migrants workers back From States.