The 4 and 6 trains are partially suspended ahead of the Tuesday commuter rush.
The MTA says there is no service on either line between Grand Central-42nd Street and Brooklyn Bridge-City Hall in Manhattan due to reports of smoke at Astor Place.
A track fire sent six MTA workers and five firefighters to area hospitals.
MTA officials say the last stop on uptown 4 train is the Brooklyn Bridge-City Hall stop, while the last stop on downtown 4/6 trains is the Grand Central stop.
Officials say 5 trains are running on the 2 line between Nevins Street and 149th Street.
The MTA says for service between Grand Central and Brooklyn Bridge-City Hall, consider taking the N/Q/R trains or the M15, M102 or M103 buses.