Police said investigators, who used sniffer dogs to examine the rubble of the four-storey building, doubted that a bomb caused the damage, although they had not ruled it out.
The building caved in on Saturday evening in Paharganj, an area of cheap hotels in New Delhi, injuring Viscount Weymouth, 21, heir to the Marquess of Bath, and killing his girlfriend Jane Kirby, 29, and his business partner, Crinan Wilde, 28.
Miss Kirby lived in Putney, south-west London, where she had worked in a variety of jobs including selling perfume. Her parents now live in the south of France. Mr Wilde, whose family live in Kingston on Soar, Nottinghamshire, had founded two companies last year and Lord Weymouth had joined him as a business partner.
Brijesh Gupta, a senior police official, said: "We cannot possibly say this was a bomb or a gas explosion or any other thing. We are keeping our options open."
Mr Gupta added that none of the victims had injuries typical of a bomb blast. "Normally bodies are ripped open, blackened and full of splinters. But all of these people died of blunt force as they were buried in the debris." Not one pane of glass in a nearby building only 15ft away was damaged.
Only one victim had burn injuries and his body smelled of kerosene. One of the survivors, a Dutchman, said he smelled gas but had not heard the deafening noise which bomb blasts usually cause.
Police said the blast also claimed three Nigerian men, two French nationals among the eight foreigners who died. None of the other victims was identified.
Two separatist groups claimed responsibility, saying they wanted to stop the Indian election. Voting begins on Saturday and ends on 30 May in Jammu and Kashmir.
However, authorities said they had never heard of the Islami Harkat-ul- Momineen, the group which issued a statement from Kashmir yesterday claiming responsibility for the blast. The statement was jointly signed by the Khalistan Liberation Force and said the bomb had been triggered by remote control and was part of an attempt to stop the elections. The elections in Jammu and Kashmir would be the first since 1989. The Himalayan state has been under federal rule since a separatist revolt in 1990. More than 20,000 people have died in the conflict.
Police were questioning a large number of people, including foreigners who survived the blast, but had made no arrests, Mr Gupta said.