Facebook is testing a personal digital assistant called "M" within its Messenger service that can answer questions with live human help and perform tasks such as buying gifts online and booking restaurants. M is "powered by artificial intelligence that's trained and supervised by people," David Marcus, vice president of Messaging products, wrote on his Facebook page on Wednesday.

Microsoft, Google and Apple are also offering digital assistants in their products, but they rely entirely on algorithms to answer questions.

M is a hybrid backed by a team of Facebook employees with customer service backgrounds, called M trainers, who can also make travel arrangements and appointments, Marcus wrote.