Subway riders faced major disruptions Monday morning after a signal problem near Carroll Street in Brooklyn caused severe delays and significant service changes on the F and G lines. 

The trouble forced the MTA to reroute a number of F trains and turn others around before completing their usual routes.

Some Manhattan-bound F trains were operating express between Church Avenue and Jay Street-MetroTech, while others were being sent over the D line between Coney Island-Stillwell Avenue and West 4th Street-Washington Square. Downtown F trains were terminating at 2nd Avenue before returning uptown. 

G train riders were also affected, with some Church Avenue-bound trains terminating at Bedford-Nostrand Avenues and turning back toward Court Square. 

The MTA advised riders traveling between Brooklyn and Manhattan to consider the A, B, C, D, N, Q, R, J, L and M lines as alternatives. Riders can also transfer between the F and the B, D and M trains at West 4th Street. 

The disruptions were also expected to cause delays on uptown D trains as they shared tracks with rerouted F trains.