At about 9:00 P.M. Peapack-Gladstone firefighters responded to 63 Highland Avenue on a reported structure fire. Upon arrival they found heavy fire and smoke showing from a large 2.5 story mansion type dwelling. Mutual aid was called immediately for engines and tankers from neighboring Somerset and Morris County Towns. The fire escalated to 5 alarms bringing in mutual aid from Somerset, Morris, and Hunterdon Counties. (3) tanker task forces were used to shuttle water to the scene for firefighting operations. The fire took over 3 hours to bring under control. No injuries were reported at the scene. Heavy snow and cold temperatures hampered firefighting efforts. The cause of the fire is currently under investigation.