This cliff fall happened in the last two weeks; at a conservative estimate 1000 tonnes of rock fell onto the beach. If you're on the beach please don't hang around this fall, don't clamber on it for fun or fossils. The cliffs are very unstable and looking at the cliffs surrounding this site there is more to fall. It will fall without warning and if you're under it you'll be as dead as the ammonites in it. Much of the fall is from the semicostatum stratum (named after the ammonite Arnioceras semicostatum that is characteristic of this layer of lower Jurassic rock) and the fossils from this bit of the beach are usually very heavily flattened and not well enough preserved to be of much value. For scale the two specks at the left of the pic are adults.
If you do see someone in trouble on the coast, call 999 and ask for the coastguard, and on Runswick beach also alert the RNLI lifeguards who are trained in first aid.