People chose any vantage point to view the draining of the lake

The channel is intended to drain about a quarter of the crater lake's rainwater into the River Bucao, thus relieving pressure on the crater's upper walls.

It took workers several weeks digging with picks and shovels to complete the five-metre deep drainage channel.

It is believed this is the first time such an operation has been carried out anywhere in the world.

More than 40,000 people from villages near the volcano were evacuated in case the attempt to drain the lake went wrong.

Click here to see drainage plan

The BBC's John McLean in Manila says that the original drainage ditch proved too shallow, so workers have begun to deepen it.

The problem has its roots in Mount Pinatubo's 1991 eruption, when 800 people were killed.

The volcano's top was blown off during the eruption, leaving a hole covering five square kilometres (two square miles).

The draining of water from the lake is expected to take several days, and the evacuees will be kept on safe ground until the operation is complete.