Boko Haram yesterday claimed it was behind the abduction of hundreds of students in northwestern Nigeria, in what appears to be a major expansion of the jihadist group's activities into new areas.

At least 333 students are still missing since the attack late Friday on the all-boys Government Science Secondary School in Katsina state -- hundreds of kilometres (miles) from Boko Haram's stronghold in northeastern Nigeria.

"I am Abubakar Shekau and our brothers are behind the kidnapping in Katsina," the leader of Boko Haram said in a voice message.

More than 100 gunmen on motorcycles stormed the rural school north of Kankara town, forcing students to flee and hide in the surrounding bush. A number of boys were able to escape, but many were captured, split into groups and taken away, residents told AFP. #BringBackOurBoys has been trending on social media since the weekend in reference to a similar hashtag sed after Boko Haram abducted 276 girls in 2014 in Chibok, in northeastern Nigeria.

The weekend attack was initially blamed on armed groups locally known as "bandits". The army has said it has located the hideout of the "bandits", and that a military operation was under way.

The Boko Haram insurgency began in 2009 in northeastern Nigeria before spreading to neighbours including Niger, Cameroon and Chad. Since then, more than 36,000 people have been killed in Nigeria and two million forced to flee their homes, sparking a humanitarian crisis in the region.