Train services came to a halt, homes and businesses were without electricity and people sweltered in humid heat as a grid failure resulted in massive power outages across Mumbai Monday morning.

As the day progressed, power restorations efforts began on war footing . Trains have started to resume operations, beginning with CR's Harbour Line. The trains are carrying only essential services workers at present, which helped minimise the passenger inconvenience.

Railway services across city on the Western Railway and Central Railway came to a grinding halt at 1005 hrs as a result of the power outage, with both the networks blaming power cut from Tata Power (their power supplier) for it.

State's Power Minister Nitin Raut said the trouble emanated from Maharashtra State Electricity Transmission Company (MSETCL) facilities during a planned maintenance work.

Tata Power, which is into both generation and distribution, attributed the power outage to a simultaneous substation tripping at 1010 hrs at state-run transmission company MSETCL's two substations in the suburbs of Kalwa and Kharghar.

Raut said power supply will resume soon, as officials were working on it on a war footing. As the afternoon progressed, power at many pockets including the Bandra Kurla Complex business district, Lower Parel and South Mumbai started resuming.

With work-from-home (WFH) becoming the norm across vital industries like banking, finance and information technology, employee output was also impacted as the residences do not have electricity backup in a city which generally has stable power.

In some instances, the snapping of power came at the most unfortunate moment, which resulted in incidents like employees in an upscale business complex getting stuck in the elevator in the times of social distancing.

After a few difficult minutes, the employees were safely evacuated, as per a video doing rounds on social media.

With the number of COVID-19 infections still very high and many patients recovering in hospitals including specially-created facilities rendering services like oxygen supply, Municipal Commissioner of Mumbai I S Chahal instructed staff to bolster diesel supply to last up to eight hours and also scout for mobile diesel generator vans which are used at film shoots as a standby.

An industry source said it took longer than expected for the power supply to resume because one of the two thermal power stations in the city and its vicinity, which have to act as a ready source as part of an islanding system to avert such situations, took longer to start generating power.

Raut said maintenance work was on in MSETCL's 400 kv Kalwa-Padgha line when the technical fault happened in circuit number 2, which was taking the entire load at the time as circuit 1 was shut.

MSETCL is responsible for getting power till the Kalwa substation from generating stations across the state, from where distribution companies like Tata Power and Adani Electricity take it to the consumers, the source said.

As part of islanding system, a thermal based power plant each of Adani at Dahanu and Tata Power (Trombay) are expected to supply power.

Restoration work in is in progress to bring supply from the three hydro units and Trombay units once the MSETCL transmission lines are connected, the Tata Power statement said.

\Another official also said that it is a grid failure, and efforts are underway to restore power supply at the earliest with the help of Maharashtra State Electricity Transmission Company and Power Grid Corporation.

Power outages were reported from suburbs like Thane, Panvel, Dombivili and Kalyan as well.

It can be noted that economic activity is limping back to normal in many parts of the country as the COVID-19 unlock process is underway. However, there continue to be many restrictions due to the need for social distancing and avoiding further infections.

BSE and NSE, the benchmark stock exchanges, which are based in the city, also reported power outages, but added that their operations were continuing normally.

A spokesperson of the Chhatrapati Shivaji International Airport said operations were normal too.