What we know about the 'house of horrors' where 11 family members were mysteriously found dead.

Indian police are unable to offer a concrete explanation of what led to 11 members of one family being found dead in their home in Delhi.

A police statement on Sunday said some handwritten notes had been found in the house “which point towards observance of some definite spiritual/mystical practices by the whole family”.

“These notes have strong similarity with the manner in which the mouths, eyes etc of the deceased were tied and taped.”

This angle was being investigated and a case of murder registered, the statement said.

The home of those who died is above a grocery store the family owned in the Burari district in a northern part of Delhi.

It is near to where three people were killed and several injured in a shootout between two gangs just two weeks ago, but police said there was no apparent link.

Sunday's dead were four men and seven women, including teenagers and a 75-year-old woman who was found on the floor.

Police said the family included the woman, her two sons and their wives, a daughter and grandchildren.

A neighbour found the victims early on Sunday, police said.

"I haven't seen such a crime before," said Vineet Kumar, additional deputy commissioner of police in north Delhi.

"We are investigating all possible angles including suicide, foul play. We can say something about the cause of death only after the postmortem reports come."

All the family members had died and there were no witnesses. Neighbours had not heard anything untoward, police said.

According to media reports, the family migrated to the capital from the northwestern state of Rajasthan about two decades ago and police were trying to get in touch with relatives there.