A warning that "ghettos" divided by race and religion could be developing in the UK has alarmed ministers.
Trevor Phillips says Britons are becoming more divided
Trevor Phillips, Commission for Racial Equality head, says a New Orleans-style separation could emerge in the UK.
In a speech this week, he will say different races and religions are leading increasingly separate lives.
Constitutional Affairs Minister Harriet Harman said the UK was "looking like America". Northern Ireland Secretary Peter Hain called the issue "worrying".
In a speech to Manchester Council for Community Relations on Thursday, Mr Philips will say that, without noticing it, UK society is "becoming more divided by race and religion".
According to the Sunday Times, he will say the "nightmare" of "fully fledged ghettos" could happen in the UK.
Former CRE head Lord Ousley, whose report into race relations in Bradford was published after riots in the city in 2001, said Mr Phillips seemed to be saying the government had "failed".
"He's right in so far as he needs to highlight the fact we do have concentrations and clusters of ethnic groups in areas that are suffering poverty, racialism, exclusion and discrimination," Lord Ousley told BBC Radio 4's Today Programme.
"It's not new, it's been around for a while," he added. "It may be getting worse."
Mr Hain, who lived in South Africa before moving to the UK as a teenager in the late 1960s, said Mr Phillips's warning had to be taken "very seriously and it is very worrying".
He said race relations had improved considerably in recent years, but added he wanted to see more integration.
He said: "It is a complex picture. On the one hand, compared to 20 years ago, certainly when I came to Britain, there is much more racial tolerance and much more integration.
"On the other hand... there is a tendency to congregate on a residential basis by your ethnic group. "
Ms Harman told the Independent that some of Britain's black and poor communities were sinking into the same underclass exposed in the US by Hurricane Katrina.
Mr Hain says there is increasing racial tolerance
"We don't want to get into a situation like America, but if you look at the figures we are already looking like America," she told The Independent.
The Sunday Times says Mr Phillips will voice his fears of a "New Orleans-style Britain of passively coexisting ethnic and religious communities, eyeing each other over the fences of our differences".
He will admit that his message is "bleak", but sees Hurricane Katrina as a warning to Britain to avoid complacently believing that it has an integrated society.
He will warn schools are becoming more exclusive and some universities are becoming "colour-coded".
And he will suggest new measures to help to encourage integration - which could include forcing "white" schools to take larger numbers of ethnic minorities.
Muslim News editor Ahmed Versi told BBC Radio Five Live the UK's problem was inequality between rich and poor rather than between races.