Much of Nigeria has come to a near-standstill after millions of workers walked out over rising fuel prices.
The streets of the commercial capital, Lagos, were reported to be deserted as a nationwide strike scheduled to last three weeks got under way.
The strike went ahead despite a court ruling ordering trade unions to stand down, and instructing the government to cut petrol prices to February levels.
The government has said it will comply, but this has not mollified the unions.
Adams Oshiomhole, president of Nigeria's biggest union, the Nigerian Labour Congress, told the BBC the strike would continue until there was evidence that the cost of petrol was actually coming down.
Police spokesman Chris Olakpe told the BBC that the situation was calm and that more than 200,000 officers had been deployed to keep the peace.
Banks and public offices are closed in the capital, Abuja.
But the strike was not universal. The Sultan of Sokoto, Nigeria's most senior Muslim leader, appealed to unions in the state of Sokoto not to strike.
This call was respected, a BBC reporter in the region said.
Oil price unaffected
There are fears that the strike could disrupt Nigeria's oil exports just one week after world oil prices hit record highs on concerns about violence in the Middle East.
OIL PRICE EFFECT
* Prices likely to rise if Nigerian exports are disrupted
* Oil firms say they have contingency plans and this won't happen
* Oil price currently falling, with US data expected to show a build in stock levels
Nigeria, a member of oil exporters' cartel Opec, pumps more than 2 million barrels of oil a day, contributing to global daily consumption of more than 75 million barrels.
Oil multinationals operating in Nigeria have said they have put in place contingency plans to ensure oil shipments continue as normal.
"Our township offices are not fully staffed, but our field oil and gas operations, including exports, are running smoothly," a ChevronTexaco spokesman told Reuters.
World oil markets were unaffected, with light sweet crude oil for July delivery - the benchmark US oil price - falling 40 cents to $36.88 a barrel amid expectations that data due later in the day would show a big rise in US gasoline stocks.
It was the first time the US oil price had fallen below $37 since late April.
However, the strike may delay the unloading of imported gasoline in the port of Lagos, where up to 11 ships are backed up waiting for a berth, Reuters reported.
Nigeria is forced to import a high proportion of its petrol and other fuels despite its abundant oil because of a lack of refining capacity.
Nigeria's latest strike was called in protest against a surge in average fuel prices from about 42 naira ($0.30) a litre to between 50 and 55 naira in late May.
Pump prices have more than doubled since June last year, when the government abolished long-standing fuel subsidies and price controls.
However, it retains the power to influence fuel prices through an oil industry 'stakeholders' committee.'
The abolition of subsidies, aimed at curbing government spending and stamping out fuel smuggling, has proved highly unpopular in Nigeria, where the bulk of the 130-million strong population subsists on less than a dollar a day.
Unions blame rising fuel prices for recent increases in the cost of food and public transport.
The fuel dispute triggered an eight-day strike, punctuated by riots which claimed 12 lives, in June last year.
The latest strike has so far been peaceful, although the Nigerian police is reported to have deployed some 22,000 officers to prevent trouble.