MADRID, May 21 (Reuters) - President Omar Bongo of Gabon, Africa's longest-serving ruler, is seriously ill in a hospital near Barcelona, a Spanish Foreign Ministry source said on Thursday.
Concerns over the health of the 73-year-old Bongo, who has ruled the West African oil-producing state since 1967, have mounted since his unprecedented move to suspend his functions as head of state earlier this month, citing the need to rest.
"He's in hospital here and currently his condition is stable but serious," the source said. Separately the Quiron Clinic in Barcelona said Bongo was there but gave no further details.
Gabonese authorities have remained silent about Bongo's state of health, but recent stays in hospital have raised questions over his succession in a country whose relative stability has been an attraction to oil and other investors.
Gabon has a tightly knit ruling elite and opposition leaders fear the president's son Ali Ben Bongo, currently the defence minister, could step in to fill any power vacuum.
A local witness said the capital Libreville was quiet on an Ascension public holiday, but some residents spoke of a public mood of uncertainty.
"We have been stocking up since we have been living with doubts over President Bongo's ability to govern the country," said 41-year-old teacher Sylvain Pounahas he shopped for food.
Others said there had been night-time army patrols in the capital although it was not clear whether they were linked to Bongo's absence from the tiny country of 1.5 million.
Economic reforms in recent years have helped push growth rates up past 5 percent, the highest in a decade, before the world downturn started hitting the oil revenues that last year accounted for half of its national output.
Aside from an oil sector with an estimated output of 273,000 barrels a day that has attracted majors such as Total (TOTF.PA) and Shell (RDSa.L), Gabon is one of the few African countries to have successfully launched a eurobond.
Analysts said any shift of power could lead to a period of political uncertainty but investors were so far not concerned about disruption of existing oil contracts or payments of its $1 billion eurobond maturing in 2017. [ID:nLK471517]
In the event of any prolonged absence by Bongo, the constitution calls for Senate President Rose Francine Rogombe -- an ally in his ruling Gabonese Democratic Party (PDG) -- to step in as caretaker and go about organising an election.
Opposition leaders have alleged irregularities in previous elections in Bongo's rule and fear that any succession could be massaged by allies to ensure the PDG retains its grip on power. (Writing by Mark John; Editing by Kevin Liffey and Giles Elgood)
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