At least two babies have died and more than 50 other babies and toddlers are being treated at Israeli hospitals after they fell ill at an unlicensed day care centre in West Jerusalem.

The three-month-old and the other about six months old were pronounced dead at Hadassah Mount Scopus hospital and Shaare Zedek Medical Centre after medics were unable to resuscitate them.

The hospitals did not specify the cause of the deaths.

Local media initially reported that one possible cause was toxic gas coming from the heating system. But the Fire and Rescue Authority said no hazardous or toxic substances had been detected.

First responders were also cited as saying conditions in the daycare were overcrowded, and one picture appeared to show an infant sleeping on a bathroom floor.