Prashant Kishor tweeted a video of migrant workers locked in a facility, weeping and begging to be freed.

Migrant workers are locked up, weeping and begging to be freed, in a video tweeted this morning by election strategist Prashant Kishor, who blamed Bihar Chief Minister Nitish Kumar for what he called a "frightening picture" of the state's handling of the coronavirus crisis.

"One more frightening picture of official efforts to protect people from the coronavirus epidemic - poor migrants who came from various parts of the country after suffering many hardships are subjected to this heart-wrenching arrangement for social distancing and quarantine by Nitish Kumar," Prashant Kishor tweeted on his former political mentor, with the hashtag #NitishMustQuit.

The video is reportedly from Siwan near the border with Uttar Pradesh, around 130 km from state capital Patna.

"Since morning, they have been telling us we will let you go, the bus is coming. But there is no bus. They are not letting us go," a man, his mouth covered with a handkerchief but jostled from all sides in the packed shed tells a reporter, weeping.

"Please help us get out. We don't want anything, just let us go," the man says, and many others around him seem to be in tears as well.

The men stick their hands out of the collapsible gate that is locked, showing papers or asking for help.

The area police said the migrants could not be allowed to move freely without some processes. "There are certain formalities like taking down all the details of individuals , medical screening and serving food before letting them go to their native areas, which requires some time...we understand people are in a hurry," said Abhinav Kumar, Superintendent of Police, Siwan.

Prashant Kishor, who was sacked from Nitish Kumar's ruling Janata Dal United in January, has been regularly posting comments and videos highlighting the problems faced by migrants during the lockdown.

After Prime Minister Narendra Modi announced a 21-day national lockdown last Tuesday, thousands of migrants across the country, abruptly left without jobs or shelter, started heading home.

Crowds of migrants have been walking with their belongings and their families, since public transport has been suspended to check the spread of the virus.

The homecoming workers pose a huge challenge to states like Bihar as the risk of the infection spreading is high.

Calling the situation "explosive", Bihar minister Sanjay Jha said the massive rush of migrants had created a big health hazard.

Yesterday, states said migrants returning home would be in mandatory 14-day quarantine.