Heena Solanki, 34, was found dead along with Prish, 4, and Jasmine, 9, at their Ruislip home in London on Friday, according to the police.
"Police were called at approximately 6.40 pm on Friday. The deaths are being treated as unexplained at this stage," a Scotland Yard spokesman was quoted as saying in the local media today.
Moments after paramedics and police arrived at the house, police ordered neighbours to close all their doors and windows, saying that there had been a "chemical incident" there, according to a report.
Heena lived with her 42-year-old husband Kalpesh's parents who had been on a holiday when the incident occurred.
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Meanwhile contradictory reports emerged in the local media with some saying Kalpesh made the grim discovery of their bodies when he returned home while some claiming neighbours called police fearing a gas leak.
Heena worked at a secondary school and would have known how to brew a killer concoction of chemicals. Last night an evidence bag marked 'caution health hazard' was removed by officers, the Mirror reported.
Some media reports claimed that Heena poisoned her daughters before killing herself in what police is terming a "toxic chemical reaction".
Shocked friends and neighbours gathered outside the house yesterday that has been cordoned off and a probe is on.
"I saw these people go into the house in chemical suits. I couldn't believe what was going on. They were a happy family and the children were lovely little kids", a neighbour said.
Another neighbour who did not want to be named, said, "Last night the police were knocking on doors telling everyone to get inside and close their windows because there had been a chemical incident".