Blast Rocks Bus Station in North Nigerian City of Kano

At least one person was killed and eight other people injured when a blast ripped through a crowded bus station in Kano, northern Nigeria, police and witnesses said on Thursday.

The explosion happened at about 3:00pm (1400 GMT) at the New Motor Park in the predominantly Christian Sabon Gari neighborhood, which has previously been targeted by Boko Haram militants.

"It was an IED (improvised explosive device). The explosive was concealed in a water dispenser and brought into the motor park by unknown people," Kano state police commissioner Adelere Shinaba told reporters at the scene.

"A woman was killed and eight other people were injured and have been taken to hospital... Our forensics experts are combing the scene for clues. We have already commenced (an) investigation."

Shinaba said there was no immediate claim of responsibility and no arrests had been made but Kano -- Nigeria's second city -- has been hit before by explosions.

On June 23, a bomb blast at a public health college in the city killed at least eight while on May 19, a suicide car bomb attack in Sabon Gari killed at least four people, including a young girl.

At least four strong explosions rocked the same area on July 29 last year, killing 12.

Blame has been attributed to the Islamist militants, who have been waging a violent insurgency in the country's north since 2009.

In the latest blast, a man who gave his name as Obi and works at a local garage, said: "A young cart pusher (porter) wheeled a water dispenser into the (motor) park and kept it near other luggage waiting to be uploaded into a bus heading to the east.

"The dispenser was given to him by two people at the gates who disguised (themselves) as travelers and asked him to bring it in for them but lagged behind him.

"The (water) dispenser exploded with a huge bang at the time passengers were disembarking from the bus close to the dispenser."

The cart pusher -- a common sight in and around bustling transport hubs in Nigeria -- had his hands and legs blown off while a woman was decapitated, he added.

Another witness, market trader Suleiman Bala, said the device was left among rows of buses and the two suspects disappeared shortly before the blast.

The latest violence came after two bombings in the northern city of Kaduna on Wednesday left at least 42 people dead and prompted the authorities to introduce a round-the-clock curfew to prevent lawlessness.

According to local police, the first attack -- a suicide bomb -- targeted the convoy of Sheikh Dahiru Bauchi, a cleric who has fiercely criticized Boko Haram's deadly five-year uprising, and left at least 25 dead.

The second attack some two hours later that killed 17 people targeted Muhammadu Buhari, one of Nigeria's most prominent opposition leaders who also ruled the country as a military dictator from 1983 to 1985.

Both bombings are in line with previous attacks on prominent Islamic clerics, whom Boko Haram accuse of co-operating with Nigeria's secular government, but also come as part of an increasing number of bloody attacks outside the group's northeastern heartland.

The capital, Abuja, has been hit three times in as many months by car bomb attacks, while there was a twin car bombing on a crowded market in the central city of Jos in May and a similar attack outside a fuel depot in the financial capital, Lagos in June.

But civilians have borne the brunt of attacks this year, leaving hundreds dead and tens of thousands more displaced in a relentless series of attacks in Nigeria's remote northeast.