About 35 million people have been left without power on the main Philippines island of Luzon.

The authorities are investigating reports of an explosion at a transmission facility. They say there is no initial indication of sabotage.

Energy Secretary Vincent Perez told a local radio station that a transmission line failed between power plants at Tayabas and Kalayaan in Laguna, just south of the capital Manila.

A presidential spokesman has urged the public to remain calm amid rumours of a destabilisation plot against the year-old government of President Gloria Arroyo.

Regular blackouts

Luzon has suffered regular large-scale blackouts in recent years, the most recent, last November, happened while President Arroyo was out of the country sparking fears of coup attempt.

Mr Perez said a helicopter was inspecting the entire length of the transmission line.

He said the line was old but plans to install a new, computerised system could take two more years to implement.

Monday's power cut left Manila commuters stranded according to radio reports. Trains ground to a halt and roads seized up as traffic lights stopped working.

A Department of Energy spokeswoman said power was being restored and the whole island could be reconnected by late afternoon.