A strong 6.1-magnitude quake has struck off the southern Philippines.

There have been no immediate reports of damage or casualties after the undersea quake struck at 2.43pm today about 62 kilometres northeast of Surigao city on Mindanao island.

The Philippine Institute of Volcanology and Seismology said the quake occurred at a depth of 26 kilometres and was felt on Mindanao's northeast tip as well as on nearby Leyte island.