NEW YORK, USA (AP) -- A new gasoline rationing plan that lets motorists fill up every other day went into effect in New York Friday morning.

Police were at gas stations to enforce the new system in New York City and on Long Island. Drivers were out before dawn to line up for their rations.

"This is designed to let everybody have a fair chance, so the lines aren't too oppressive and that we can get through this," Mayor Michael Bloomberg said.

The gas rationing plan took effect at 5:00am Friday on Long Island and at 6:00 am in New York City. Officials said it was imposed because something had to be done to ease the long waits for fuel, which they say has caused panic-buying and hoarding.

Bloomberg said only a quarter of the city's gas stations were open. Some were closed because they were out of power, others because they can't get fuel from terminals and storage tanks that can't unload their cargoes.

Gas will be available to drivers with licence-plate numbers ending in an odd number or a letter on Friday. On Saturday, drivers with license plates that end in even numbers or zero can fuel up.

Buses, taxes and limousines, commercial vehicles and emergency vehicles are exempt from the plan, as are people carrying portable gas cans. Vanity plates that don't have numbers are considered odd-numbered plates. Out-of-state drivers are also subject to the system.

Bloomberg said the shortages could last another couple of weeks.