Angry protesters attacked banks Tuesday in a southwest Nigeria city over a cash shortage, police and residents said, as tensions flare in the country three weeks before a presidential election.

Africa's most populous country has been crippled by fuel shortages for weeks, and cash dispensers are running empty after a sudden currency swap.

This has led to long lines outside banks and fuel stations, and tempers are flaring.

In southwest Abeokuta, police said riots broke out in three parts of the city after customers waited hours to withdraw cash to no avail.

"Unfortunately, some hoodlums hijacked the protests and started destroying and vandalising bank properties," state police spokesman Abimbola Oyeyemi told AFP.

He said workers and the properties of two commercial banks were attacked, and that protesters had lit fires on roads to disrupt traffic.

"The situation is under control. But we are warning hoodlums and criminals to desist from causing mayhem in the state."

Local residents said the police fired shots to disperse the protesters, who pelted them with stones, iron bars and planks. Police deny this.

In October, the central bank announced, with no warning, that it was changing banknotes in a bid to combat inflation and tackle the number of counterfeit bills circulating in the country.

However, the sudden change caused long queues as Nigerians rushed to beat a deadline to turn in old notes, which has since been extended.

A lingering fuel shortage is also stoking anger.

While Nigeria is one of Africa's largest crude oil producers, it has almost no refining capacity and must import fuel from Europe and elsewhere.

The situation has led to a hike in pump prices with Nigerians spending hours in queues to fill up.

There have been protests in some cities nationwide. Last week, one person was killed in south-western Ibadan when an irate crowd clashed with the police.

Two weeks ago, riots broke out in Kano, northern Nigeria's largest city during a visit by President Muhammadu Buhari.

Nigerians will go to the polls on February 25 to elect a successor to Buhari, who will step down at the end of two terms in office.