UPDATE 6:39 P.M.: One southbound lane has been opened after a tractor trailer caught fire near mile marker 129 on I-81.

The backup on I-81 southbound is about eight miles long.

ORIGINAL STORY: A vehicle fire is causing delays on I-81 southbound.

A tractor trailer is on fire at mile marker 129 in Montgomery County. This incident is about 0.6 mile north of Exit 128.  

All southbound travel lanes closed.