A loud explosion hit a crowded shopping centre on Wednesday in Nigeria's capital Abuja, which has been repeatedly attacked by Boko Haram Islamists, the national rescue agency said.

"We received the information at about 4:00 pm (1500 GMT) about a blast" at the Emab Plaza, not far from the seat of government, said Manzo Ezekiel, spokesman for the National Emergency Management Agency (NEMA).

"Rescue operation has already commenced," he told AFP. "You can see smoke billowing from the sky. It's a very crowded place. It's full of people on a working day."

An employee of the nearby Newcastle Hotel in the Wuse II area of the city, who did not want to be named, said she clearly heard the explosion.

It was not clear what caused the blast but Boko Haram has attacked Nigeria's capital twice in the last 10 weeks.

A car bombing killed 75 people at the Nyanya bus terminal on the outskirts of the city on April 14 while a copycat bombing at the same spot on May 1 left 19 people dead.

Soldiers and police cordoned off the scene of the blast and firefighters were at the location, as thick smoke billowed into the sky, an AFP reporter on the ground said.

AFP