This paper discusses methods for estimation of area's frequency response characteristic (AFRC) during large frequency changes. The operating point changes significantly during such transient events; consequently the estimation method should adapt to the time-varying nature of the AFRC. Moreover, available measurements have a poor time resolution and are considerably contaminated by errors. Therefore, new estimation methods are proposed that are based on local correlation between the frequency deviation and interchange power variation measured on all area's tie-lines. The presented estimation methods were compared with a classical approach that is based on the ratio of mean changes as well as with conventional least squares parameter estimators. Extensive numerical simulations and field measurements were applied for performance evaluation, where the obtained results show robust and satisfactorily accurate responses of the proposed estimation methods.