LAGOS (Reuters) - At least 18 people, 12 of them school children, were killed when the bus they were travelling in crashed on a busy highway in the southern Nigerian state of Delta, media reports said on Saturday.

The 18-seater bus was conveying pupils from Agbor town to Benin city in neighbouring Edo state for an inter-school debate on Friday when it crashed head-on with another vehicle that had veered into its path after bursting a tyre, the Guardian newspaper said.

"Only four people in the students' bus survived," the paper said, quoting an officer at the crash scene along the Benin-Asaba express-way. All the four passengers in the other vehicle also died in the accident.

Nigerian roads are among the deadliest in the world because of large potholes, poorly maintained vehicles and dangerous driving.

At least 5,000 people die on Nigerian roads every year, according to the police.

Most motorists in Africa's most populous country have never taken driving lessens as a licence can easily be obtained with a test -- for less than $50.

At least 45 soldiers who had just returned from peacekeeping in Sudan's Darfur region, were killed in May when a petrol truck hit their military convoy on a high-way in northeastern Nigeria.