Lagos - Results in Nigeria's governorship vote saw a swing towards president-elect Muhammadu Buhari's All Progressives Congress (APC) party on Monday, two weeks after it made history by unseating the incumbent in a presidential poll.Eight states have so far abandoned the People's Democratic Party's (PDP) of defeated president Goodluck Jonathan in favour of the APC - which now has a total of 20 states, more than half of the territories up for grabs against the PDP's 13.The results completed an unprecedented shift in Nigerian politics, away from the PDP which has dominated since the end of military rule in 1999. These elections mark the first time since independence from Britain five decades ago that a ruling party has been forced out by the ballot box.Nigeria's 36 state governors are among the most powerful politicians in the country, controlling budgets bigger than those of many African countries and wielding influence that can decide which candidates go on presidential tickets.Jonathan's supporters took some heart by holding onto the strategically vital southern oil hub of Rivers state, in a landslide victory announced on Monday. The governorship polls were held in just 29 states on Saturday, since seven had already been settled in by-elections over the past few years.Buhari, who won a decisive victory in the March 28 presidential poll and a majority in both legislative houses, takes power on May 29.As in past governorship polls, these ones were marred by violence, intimidation and reports of fraud. Observers said they were dirtier than the presidential ones, particularly in the oil-producing delta region's Akwa Ibom and Rivers states - but better technology meant there was less outright fraud than in past gubernatorial polls. At least ten people were killed in violence across the country.The US embassy congratulated Nigeria for an electoral process that it said "generally went well across the country.""We have seen the reports of violence and alleged irregularities... and call on those dissatisfied to pursue their grievances peacefully in the judicial arena," it added.Around 100 people gathered in the capital of Abia state, in the Niger Delta, to protest against alleged fraud on Monday.One state remained with the minor opposition All Progressives Grand Alliance party, while one was deemed inconclusive and one had yet to be announced by the electoral commission by Monday by 12:30 (11:30 GMT).