Hear'Say's Mylene Klass spoke to the audience
Sting, who was to perform live via a webcast from Italy, announced he was not to play a full concert.
According to reports, the star performed just one song, Fragile, before asking for a minute's silence.
Sting said: "This was to be a very joyous occasion tonight.
"Because of the horrific events of today, it simply can't be a joyous occasion.
"We'd like to have one number on the webcast for the rest of the world to see and then shut it off as a token of respect to those who've lost their lives and those who've lost loved ones in this terrible event.
"I'd like a minute's silence after that song."
A spokeswoman for the band said they had been due to fly to New York on Wednesday.
Tribute
Tricky also cancelled a London show on Tuesday night.
Promoters issued a statement saying: "Following terrorist attacks in the United States, the Gap Hi-Fi event at Atlantis II featuring Tricky has been cancelled.
"Our thoughts are with the families of the victims."
Britney Spears, who is now in Australia after being en route there at the time of the attacks, said she was dedicating the trip to the victims of the tragedy.
The singer also issued a press release, published on her website, expressing her sympathy.
"I would like to dedicate my time here in Australia to all those who lost their lives in this tragedy and their families and friends who continue to suffer," she said.
The singer also cancelled a press conference in Sydney, planned to launch her third album.
"Words can't describe how I feel right now. I will be continuing with my schedules here in Australia as planned, but I'm sure all of you will understand the decision that has been taken under the current circumstances," she added to explain the changed plans.
Silence
Tickets to forthcoming U2 concerts which were set to go onsale this weekend have been postponed.
According to the U2 website the concerts, which were set to begin in Indiana in October, are still to go ahead.
"For the moment this is the only change," the site says.
"We'll keep you posted on any further changes to the onsale calendar."
Pop band Hear'Say asked fans to observe a minute's silence for the victims at the start of Tuesday's concert at the London Arena.
"Our thoughts go out to the people who have the heinous task of finding the terrorists and bringing them to justice," said singer Mylene Klass.
The five singers, who were brought together by the ITV show Popstars last year, bowed their heads during the silence.
Wednesday nights BMI awards ceremony, at which Pete Townshend was due to be honoured, has been postponed "out of respect for the events in the United States".