A large grassfirenorth of Werribee has been deemed under control after the CFA earlier issued a 'watch and act' alert for surrounding areas including Tarneit and Truganina.

About 36 CFA and MFB trucks battled the 80 hectare blaze at Shannahans, Dukelows and Dohertys Roads in Mount Cottrell, about 34 kilometres west of Melbourne's CBD.

A large grassfire is burning out of control north of Werribee, with the CFA issuing a 'watch and act' alert for surrounding areas including Tarneit and Truganina. Credit:Craig Abraham

Firefighters were called to the scene about 5.30pm on Wednesday following reports of an out of control large grassfire.

By 9pm the fire was declared under control.