Indian police are investigating the deaths of 11 people from one family whose bodies were discovered in a house in the north of Delhi.

Officers arrived at the property in Burari at about 7.30am on Sunday after receiving a call from a neighbour saying that several people may have killed themselves.

They found 10 bodies, including two 12-year-old children, and a 75-year-old woman.

There were no signs of forced entry into the house. Police said in a statement they had found handwritten notes that pointed “toward observance of some definite spiritual or mystical practices by the whole family”.

The dead included Narayan Devi, her sons Bhupi, 46, and Lalit, 42, along with their wives and children, and Devi’s daughter, Partibha, 60, and her daughter.

Members of the family had lived in the home for nearly three decades and had celebrated the engagement of Partibha’s daughter, Priyanka, two weeks ago.

Crowds gathered on Monday morning inside the narrow alley leading to the two-storey home.

Among them was Dileep Singh Chauhan, the brother of Bhupi’s wife, Swita. He said he last spoke to her on Thursday. “She was perfectly happy. I did not feel any tension,” he said.

He said the family were practising Hindus and had a small shrine in the home but that his sister was not especially devout. “She was not very into religious things, not at all,” he said.

A neighbour, Draupdi, said she had seen the family celebrating Priyanka’s engagement recently and “everything was normal”.

She said she had visited the general store the family ran from their house on Saturday evening, hours before they were found dead, and found nothing amiss. “They were not a violent family; they never even screamed at their children if they were making noise, they were not that kind of people,” Draupdi said.

“People who say this was black magic are wrong, it is just rumours, there is nothing of that kind,” she added.

Police have registered a murder case but are understood to be investigating the possibility of suicide.

The Delhi chief minister, Arvind Kejriwal, said the incident was tragic. “Police are investigating,” he said after visiting the scene. “Let’s wait for their investigation to be over.”