A major power breakdown owing to a grid failure brought bustling Mumbai and parts of the Mumbai Metropolitan Region of Thane, Raigad and Palghar districts to the knees on Monday, officials said here.

Rattled by the outrage over the outage, Chief Minister Uddhav Thackeray and Energy Minister Niting Raut ordered a high-level probe into the incident, even as supply limped back to normalcy by 2 p.m.

Raut said that some regular maintenance work was going on at the 400KV lines in Kalwa, Thane.

"There was some routine maintenance work underway on Circuit 1 of MSETCL's 400 KV Kalwa-Padgha GIS centre. So the entire load was shifted to Circuit 2. But because of a sudden technical glitch, large parts of Mumbai and Thane were affected," Raut said in a video statement.

The situation was complicated with multiple trippings on the Kalwa-Padghe and Kharghar lines (Thane) and the transformers that supply power to Mumbai, resulting in total disruption of around 2,200 MW of power supply to the country's commercial capital for several hours.

Even as angry Mumbaikars vented their ire on social media and the Opposition Bharatiya Janata Party (BJP) slammed the government, Thackeray convened an emergency meeting with Raut, MoS Energy Prajakt P. Tanpure, Chief Secretary Sanjay Kumar and Energy Secretary A.K. Shrivastava before ordering a probe into the outage and a technical audit of the Energy Department.

Anticipating an ugly situation in Covid times, BMC Commissioner I.S. Chahal directed all hospitals to stock sufficient diesel for at least hours for generators to ensure no power failures, especially in the ICUs, and to give their status reports to the control rooms every half an hour.

One of the Mumbai distributors, BEST, said the power supply was "interrupted due to TATA's incoming electric supply failure" at around 10.15 a.m.

The power breakdown hit the lifelines of Mumbai -- Central Railway and Western Railway -- with all local trains halting enroute till Vasai and Diva.

Hapless commuters at many locations jumped off the trains and started walking towards the nearest suburban railway station as trains remained suspended between Churchgate-Borivali and CSMT-Thane during the power breakdown period.

Since power supply from MSETCL was available at Vasai Road, the WR managed to operate essential suburban trains on the Borivali-Virar sector, said spokesperson Sumit Thakur.

By 12.30 p.m., spokespersons of both CR and WR announced that services had resumed and would soon be back to normal operations.

All operations at the Chhatrapati Shivaji Maharaj International Airport were normal, said a spokesperson for Mumbai International Airport Ltd.

The Bombay Stock Exchange and the National Stock Exchange functioned normally with backup power arrangements, officials said, though some brokers and broking houses experienced trouble during peak trading hours.

For the first half, all industrial, business and commercial activities in the MMR ground to a halt and picked up gradually as power was restored in phases by 3.30 p.m. after nearly 9 hours of daytime 'blackout' in spurts since 7 a.m.

The power failure had other repercussions like hitting water supply schedules, elevators in some buildings, and traffic signals, leading to chaos on roads, among others.

Tata Power Company said that as per the preliminary assessment, on Sunday the MSETCL's 400KV Pune-Kalwa line was under forced shutdown, and on Monday morning at around 6.45 a.m., an emergency shutdown was ordered for the 400KV Kalwa-Padghe line-1 to rectify the problems.

At 9.58 a.m., the Kalwa-Padghe line-2 carrying a load of 633 MW tripped, thus increasing the flow on the Pune-Kharghar to 900 MW, but it also tripped two minutes later, hitting Mumbai.

Mumbai's unique 'islanding system' usually prevents it from such major blackouts, but yet it could not bear the additional 900 MW load and collapsed at around 10.05 a.m.