Nigerian motorcyclists have taken to wearing dried pumpkin shells on their heads, in the wake of a new law that forces them to wear helmets.

Police in the northern city of Kano said they had stopped several bikers with "improvised helmets", after the law was introduced on January 1st..

The law has been strictly enforced, with police impounding thousands of motorbikes.

Yusuf Garba, Kano Federal Road Safety Commission commander, explained to AAP that police were taking a hard line with people found using the improvised helmets.

"We are impounding their bikes and want to take them to court so they can explain why they think wearing a calabash [pumpkin shell] is good enough for their safety," he said.

In Kano city alone, fifty motorbikes had already been seized , he added.