Ten newborns were killed on Saturday in a massive fire at a hospital in Maharashtra, India's richest state, a doctor said, as leading politicians expressed grief at the loss of life.

"The fire broke out at 2 a.m. (2030 GMT) today," said Pramod Khandate, a civil surgeon at Bhandara District General Hospital in the western Indian state. 

Rescue efforts were hampered by continuous blasts inside the ward, according to local media reports. Seven of the 17 children in the Sick Newborn Care Unit were rescued, Khandate told Reuters partner ANI. 

"Hospital authorities have rescued seven babies but 10 have died in an unfortunate incident," Khandate told reporters.

Some of the babies were only a few days old, and the oldest three months.

The cause of the fire is not yet known but the hospital administration said an electrical short-circuit could be the possible reason.

Prime Minister Narendra Modi described the incident as a "heart-wrenching tragedy."

"Heart-wrenching tragedy in Bhandara, Maharashtra, where we have lost precious young lives," Modi said in a tweet. "My thoughts are with all the bereaved families. I hope the injured recover as early as possible."

India's Home Affairs Minister Amit Shah said he was "pained beyond words" over the "irreparable loss."

Defence Minister Rajnath Singh said he was "deeply saddened" by the deaths, adding: "My heartfelt condolences to the bereaved families."

(With input from agencies)