Police say they have not identified any specific targets. However, the BBC understands that images found during searches showed the Arndale and Trafford Centre shopping complexes, Birdcage nightclub and St Ann's Square.
Staff at the Arndale and Trafford Centres said they had not been informed of any threat and that stores were operating as normal over the Easter weekend.
Police are not thought to have recovered any explosive devices during their searches. BBC security correspondent Frank Gardner said his understanding was that the alleged plot had been at the "aspirational, not operational" stage.
Meanwhile, critics of the UK's border controls have pointed to alleged deficiencies within the student visa system and the fact that 10 of the suspects had such visas.
Latest Home Office figures show that between April 2004 and April 2008 about 42,000 Pakistani nationals entered the UK on student visas.
Conservative shadow home secretary Chris Grayling called on the government to "urgently step up" background checks on students from countries linked to terror.
The chairman of immigration campaign group Migrationwatch UK, Sir Andrew Green, said "inadequate" checks on student visas had left a "gaping hole" in Britain's borders.
"Applicants from countries of concern like Pakistan and North Africa should be given a full interview by a UK-based visa officer and only admitted if they can demonstrate that they are genuine," he said.
Former London Mayor, Ken Livingstone, said terrorists would "find a way around" any changes to the visa system.
"We catch these people because of electronic surveillance and double agents and we aren't going to pick one up easily at the border," he said.
Footage of police raiding a flat in Cheetham Hill on Wednesday
The Home Office says the UK student visa system was tightened in September 2007.
Pakistani applicants went through vetting procedures such as fingerprint tests and checks against criminal and counter-terrorism databases, a spokesman said.
From autumn this year, British universities will also be obliged to check the names of overseas students against a government database of terror suspects.
It is unknown whether any of the suspects arrested on Wednesday applied for their visas after September 2007.
After Wednesday's raids Prime Minister Gordon Brown challenged Pakistan to do more to weed out potential extremists who might target the UK.
Immigration minister Phil Woolas then rejected criticism from Pakistan's High Commissioner, Wajid Shamsul Hasan, who accused the UK of refusing help with background checks.
A Downing Street spokesman has since confirmed that Mr Brown and President Asif Ali Zardari have spoken on the telephone and agreed "the UK and Pakistan share a serious threat from terrorism and violent extremism".
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