More quakes and gas emissions have been detected from a volcano on an island close to the Philippine capital, possibly indicating an eruption is looming, the government said on Saturday.

Twenty volcanic quakes were detected at Taal Volcano in the 24 hours to Saturday 8:00am (0000 GMT) compared to 15 quakes in the same period on Friday, indicating that magma is still rising to the surface, the volcanology institute said.

Additionally, the water in the crater of Taal is heating up while the volcano's emissions of carbon dioxide have risen from 1,875 tonnes per day in February to 4,670 tonnes by the end of March.

"If this trend continues, we may have to raise alert level again," said Paul Alanis of the Philippine Institute of Volcanology and Seismology (Phivolcs).

People were warned not to approach Taal's crater or parts of its slopes where gas could still vent out.

Phivolcs on April 9 raised the second of a five-step alert around Taal Volcano, a popular tourist attraction 65 kilometres (40 miles) south of Manila, after detecting signs that magma was rising to the top of the volcano.

However Alanis said this does not mean an eruption is imminent and that the volcano might yet stabilise.

Despite government pleas for people to leave the 2,500-hectare (6,178-acre) crater island, only 163 of the estimated 7,000 people living there have evacuated, the civil defence agency said in a statement.

Taal is one of the most unstable of the country's active volcanoes with 33 recorded eruptions, the last one in 1977.

The lake surrounding the crater prevented deaths in 1977 and during other eruptions, as the body of water protected outlying areas from the lava.