Schools and businesses shut across the Philippine capital on Monday as a volcano belched clouds of ash across the city and seismologists warned an eruption could happen at any time, potentially triggering a tsunami.

Thousands of people were forced to evacuate their homes around Taal, one of the world's smallest active volcanoes, which spewed ash for a second day from its crater in the middle of a lake about 70 km (45 miles) south of central Manila.

More than 24,000 people have been evacuated from the volcanic island and the area immediately around it - normally a popular tourist spot.