Widespread inefficiency and fraud are putting Nigeria's voter registration at risk, according to opposition parties.

The Alliance for Democracy reported "irregularities which can mar the entire exercise and defeat its very purpose", according to the Associated Press news agency.

Among the reported problems were the moving of registration stations without notice, a lack of registration forms and the registration of "ghost voters", who were either under-age or had already been registered.

The electoral commission itself reported problems in Plateau State where officials were unwilling to ask Muslim women to remove their veils, even when they suspected they were not old enough to register, according to the Guardian newspaper.

They don't ask for identification, anybody can say they are anyone.

Gani Fawehinmi, human rights lawyer

The massive task of registering voters in preparation for state and national elections began on 12 September and will continue to 10 days.

Election officials said on the first day of the process that registration started smoothly at 120,000 centres and they were confident of enfranchising the country's 60 million voters.

In some areas of the country, there has been praise for the commission's work - the Governor of Borno State describing the registration as a huge success.

Nigeria's electoral roll is years out of date

But there were complaints from the start from the northern Nigerian state of Nassarawa that no registration was taking place in some areas. The Governor of Katsina State also criticised the process, saying that too few forms had been supplied.

The BBC's Sola Odunfa in Lagos reported that registration was slow in Nigeria's commercial capital and many people chose to stay at work on the opening day

But the complaints have become more serious.

Child voter

"Corruption is fast creeping into the whole exercise," according to the human rights lawyer, Gani Fawehinmi.

He said that he had been unable to register when he had tried on Monday, because the registration centre which he visited had no forms.

"We are collecting reports all over. Multiple registration is not being properly prevented.

"They don't ask for identification, anybody can say they are anyone," Mr Fawehinmi said.

Katsina State Governor Umaru Musa Yar'Adua told journalists at government house on Monday that the whole exercise could be a failure if the commission did not supply enough registration materials.

He said up to 40% of the state's voters would be left unregistered if action was not taken.

The Associated Press reported from a registration centre in Abeokuta, south-western Nigeria, that officials there had registered a male named Dele Ogulowo, who looked no more than 10 years old.

He was registered less than an hour after President Olusegun Obasanjo had visited the centre to check on the registration.

In Plateau State, the state's electoral commissioner, Alhaji Isyaku Maigoro, said that veiled Muslim women had tried to register without unveiling to show their faces.

Some electoral officials, he said, had been unwilling to ask them to unveil and had registered them even when concerned that they were not old enough to vote.

He told the Guardian newspaper that this had been done to avoid "social strife", but he asked women to briefly unveil when registering

Buying registration cards

AP also cited a businessman in Kano, northern Nigeria, as saying that newly-registered voters could be seen wiping the indelible ink from their thumbs after registering.

The ink is there to prevent people registering more than once.

The businessman, Amadi Chike, added that he had seen people buying registration cards from voters for 150 naira ($1.15).

In some areas of Nigeria, international observers reported the registration of double the number of voters that officials had expected to live in certain districts.

Obasanjo is facing possible impeachment

But election observers, cited by news agencies, have said that a "few lapses" would not affect the overall registration process.

In the Bakassi district of Cross River State, the electoral commission has moved to avert problems of insufficient centres by providing 10 mobile registration booths and taking on extra staff.

Presidential elections must come before the current term of President Olusegun Obasanjo - now threatened with impeachment - ends in May.

The electoral commission has called on all voters to register and to see it as the first part of the elections.