A road has been closed after a landslide caused a tree to fall and block the carriageway near Neath.
Police have warned driver to find an alternative route with Glynneath Road closed in both directions.
Heavy rain has led to travel disruptions across Wales.
Drivers have been warned of poor driving conditions on the M4 because of surface water and police are conducting road safety tests on routes.
Rail travel has been impacted too with services suspended between Machynlleth and Newtown because of flooding.
The Met Office issued a yellow weather warning for rain in Wales for today.
The warning runs from 12am until 6pm, with most of the country being affected by the heavy downpours.