Council inspectors in south London have discovered 600 asylum seekers living in cramped conditions in a 98-bedroom hotel in Crystal Palace.
Housing officials were alerted to the situation when neighbours of the Queens Hotel on Church Road complained about anti-social behaviour and noise coming from the building.
One room had nine people sleeping in it, while most of the en suite rooms housed up to four individuals, Croydon Council's housing enforcement team revealed on Thursday.
Local MP Steve Reed said: "The hotel is on the edge of our small but thriving shopping centre in a highly residential area. It seems highly inappropriate to place so many asylum seekers in an area like this without warning or preparation."
Reed called on immigration minister James Brokenshire to take action. "I am demanding an urgent meeting to discuss local residents' concerns", he said.
"I am worried about the safety of the people living in the hotel, the sudden conversion of the hotel into a bed and breakfast hostel without consultation and the impact of an extra 600 people suddenly arriving in the neighbourhood."
A Home Office spokesman said: "We are taking urgent steps with our housing providers to reduce the number of people living at the Queens Hotel in Crystal Palace.
"We have ensured that the numbers in accommodation at this location meet appropriate requirements."