It's as yet unknown how many casualties have resulted as no doubt a massive emergency response is underway.

Indeed close-up images just before the larger blast shows a large complex on fire, with either ammunition or fireworks going off, followed by the intense shockwave.

The AP describes the aftermath:

The explosion appeared to be centered around Beirut's port and caused wide scale destruction and shattered windows miles away.

An Associated Press photographer near Beirut's port witnessed people wounded on the ground and widespread destruction in central Beirut.

Some local TV stations reported the blast was at Beirut's port inside an area where firecrackers were stored.