"The latest information we have is that the boat, which had around 200 immigrants aboard, overturned," a Maltese navy spokesman told AFP, saying rescue boats and helicopters had been sent to the site around 130 kilometres north of Malta.
"The operation is in progress. The navigational conditions are difficult, with strong wind," he added.
An Italian coast guard commander confirmed the incident.
"It was a shipwreck in Maltese territorial waters. We are helping the authorities from Malta. We do not know yet if there are any deaths," Filippo Marini told AFP.