HOUSTON -- Unseasonably hot temperatures forced power utilities around the Houston area and Texas to conduct rolling blackouts on Monday.

As temperatures climbed into the upper 90s and above 100 for another day, the Electric Reliability Council of Texas Inc., which runs Texas' electricity grid, declared an emergency situation and ordered the blackouts because of the lack of electricity around the state.

ERCOT said it declared the emergency after concluding there was insufficient generating capacity in the region to reliably serve the public's electricity demand.

As much as 15 percent of the state's power supply goes off-line each spring so plants can perform seasonal maintenance before energy usage peaks in the summer, said Public Utility Commission spokesman Terry Hadley. He said maintenance is typically finished by mid-May.

But unusually high temperatures this spring have pushed demand for electricity, creating a shortage, he said.

The rollouts were limited to the ERCOT grid, which provides electricity to about 80 percent of Texas.

CenterPoint Energy spokeswoman Emily Mir Thompson said rolling blackouts every 15 minutes for the Houston area were ordered just after 4 p.m. Monday.

"ERCOT requested that 1,000 megawatts of load be dropped throughout the state of Texas, so CenterPoint Energy represents 26 percent of that load. So, we started periodically dropping customers in 15-minute intervals on a rotating basis in our service area," she said.

Austin Energy said it began its rotating blackouts about 4:20 p.m. to comply with our share of the load shedding requirement.

ERCOT urged customers around the state to curtail their use or electricity to the lowest level possible, including setting their thermostats at 78 degrees or higher and not using electric lighting, appliances or equipment unless absolutely necessary for health or safety.

To find out the current load on the grid, visit http://mospublic.ercot.com/ercot/jsp/frequency_control.jsp.