LIBREVILLE (Reuters) - A strike by Gabon's main oil industry trade union has brought public transport in the capital Libreville to a standstill as fuel stations began running dry on Thursday, a Reuters witness said.

Gabon's government overnight called on the ONEP union to return to negotiations over labour regulations and put off the strike in the interests of the country and the economy, but ONEP rejected the order as unserious.

The strike in Gabon, Africa's seventh-largest oil producer, with an output of some 250,000 barrels of crude oil per day, is one the biggest tests for President Ali Bongo since he replaced his father as president last year.

Residents in Libreville, whose 600,000 inhabitants account for roughly 60 percent of the entire population of Gabon, had been stockpiling fuel ahead of the strike.

But fuel stations began running out overnight and the lack of taxis left crowds of people stranded on pavements, although it was not immediately clear if oil production had been affected by the strike.

"We will never be able to satisfy everyone," said a pump attendant at one petrol station that still had fuel on Thursday. "By midday, there won't be a drop of petrol or diesel in Libreville."

ONEP said on Monday it had broken off discussions with the government in a dispute over labour regulations, notably a requirement to provide minimum service in the sector -- a rule unionists says breaches a basic employee right to strike.

Labour minister Maxime Ngozo Issondou said late on Wednesday that the strike should be called off in the interests of the Gabonese people and the economy.

The government would take a number of steps, including re-launching the commission aimed at resolving the impasse and establishing temporary restrictions on foreigners working in the oil sector, as soon as the unions returned to negotiating table, Ngozo Issondou said.

But ONEP spokesman Arnaud Engandji said the government's invitation was "not serious".

"If the government wants to see us around a table, they should address us through the appropriate channels" he said.

Gabon enjoyed relative political stability under the late president, Omar Bongo, who used decades of oil production to buy off opponents and create jobs through a bloated bureaucracy.

But after winning a disputed elections last August, Ali Bongo has vowed to reform the nation's economy and make it less dependent on oil as output declines.