MANILA -- The operator of Luzon's power grid placed the Philippines' main island on the second-highest power supply warning on Thursday due to insufficient reserves, distributor Meralco said.

Yellow Alert, one step below red alert, will be in place from 10:01 a.m. to 11 a.m.; from 1:01 p.m. to 4 p.m.; and from 5:01 p.m. to 7 p.m., Meralco said, quoting the National Grid Corp (NGCP).

The NGCP is a private firm that operates the grid, the system that connects power plants to distribution utilities.

Meralco advised customers to conserve power. Commercial establishments may be asked to switch to generators in case of a supply deficiency, it said.