The fire broke out at the Hotel Arpit Palace in a congested part of central Delhi, with images showing it engulfing the entire top floor.
"We have confirmed with hospital authorities, the toll is now 17 including a child," Sunil Choudhary, a fire brigade official, told AFP.
Local media reports said the woman and the child died as they tried to escape by jumping from a window.
G.C. Misra, Delhi fire brigade director, said the blaze had been brought under control and that 35 people were rescued by firefighters in an operation lasting several hours.
"There was wooden panelling on corridors because of which people could not use corridors to evacuate," another fire officer told reporters.
Images showed thick smoke and flames billowing out of the top floor of four-storey hotel, popular with budget travellers.
Police said they were investigating the cause.
The blaze was extinguished in the early hours with the help of at least 25 fire engines, with the top floors being gutted.
Fires are common across India because of poor safety standards and lax enforcement of regulations.
Activists say builders and landlords often cut corners on safety to save costs and have accused civic authorities of negligence and apathy.
Fire disasters are particularly frequent in Mumbai, India's financial capital where millions live in cramped and dilapidated properties because of high rents.
In December, eight people were killed when a fire engulfed a hospital in Mumbai.
In 2017, 14 people were killed, also in Mumbai, when a huge blaze tore through a popular restaurant.