At least 19 people have died after a magnitude-7.8 earthquake struck off the coast of Mindanao island in the southern Philippines, officials say.

The quake occurred on Monday at 07:37 local time (Sunday 23:37 GMT), triggering tsunami alerts in the Philippines, Indonesia, Japan and Australia. Some of those were cancelled hours later.

Videos and images showed buildings collapsing, including a clip of a Jollibee fast food restaurant reduced to rubble.

At least 134 people were reportedly injured across several provinces - South Cotabato, Sultan Kudarat, Sarangani - and the city of General Santos, a local official said. These numbers still need to be verified by the national disaster agency.

The official count from the agency - the National Disaster Risk Reduction and Management Council - typically comes about a day after the incident. They tabulate all the numbers given by various sources including the police, local officials and disaster relief agencies.

Philippine President Ferdinand Marcos Jr said in a statement that agencies were coordinating their disaster response.

"The national government is moving and we will not leave Mindanao behind," he promised.

Marcos also ordered the suspension of classes in affected areas after the quake, which coincided with the first day of the school year in the Philippines.

In one video posted by a primary school in Davao Occidental province, dozens of terrified students can be seen squatting on the shaking ground.

The video also showed a corrugated-roof shelter collapsing behind them, though the school said in its post that no-one was injured.

More than 130 aftershocks, with magnitudes ranging from 1.3 to 6.7, were recorded after the initial quake.

In the coastal province of Sarangani, the quake temporarily downed power and communication networks - though they were later restored.

General Santos, the city near the quake's epicentre, is known as the Philippines' tuna capital. It's also known as the hometown of Manny Pacquiao, the world boxing champion who later became a politician.

Earthquakes are common in the Philippines, which sits on the geologically unstable "ring of fire". While most of these quakes are minor and pass relatively peacefully, some have proven deadly: Last September, a magnitude-6.9 earthquake struck the central Visayas region, killing more than 70 people.

Shortly after the quake on Monday morning, authorities in Japan warned of one-metre-tall tsunami waves reaching its shores.

A tsunami wave measuring a few centimetres was later observed in the southern prefecture of Okinawa, while a 20cm (0.7ft) wave was measured in the distant Ogasawara Islands, authorities said.

Waves were also detected at several locations along the coasts of Indonesia, Palau and the Philippines. The height of those waves ranged from a few centimetres to 1.4m (4.6ft), according to authorities.