At least eight people died and "
The coastguard said one of its boats had recovered seven bodies and another person had died on a rescue boat operated by Malta-based charity MOAS and the Red Cross.
The Red Cross said survivors' accounts suggested "many" people were unaccounted for, including the mother of a young girl who was among the traumatised survivors on MOAS's boat, the Topaz Responder.
"There may be many missing, many dead," Red Cross Team Coordinator Abdelfetah Mohamed said in a telephone call to colleagues that the humanitarian organisation posted on YouTube along with still images of the aftermath of the rescues.
"The doctors managed to revive several people with hypothermia but it was too late for one of them," MOAS spokeswoman Maria Teresa Sette told AFP.
The coastguard said a total of around 1,200 people had been rescued during operations overnight and on Tuesday morning to rescue people on board 11 boats.
One wooden vessel was carrying 450-500 people. There were also two smaller wooden boats as well as the usual overcrowded inflatable dinghies.
The latest victims will add to a total of 4,655 migrants confirmed to have died or disappeared in the Mediterranean so far this year, according to counts by the International Organisation for Migration and the UN refugee agency.
The rescued survivors will add to a total of 168,544 migrants who have landed in Italy this year, which is set to be a record one for arrivals. The vast majority of them come from Africa and have begun their crossings from Libya.