qmake and QT_INSTALL_PREFIX. How can I select a new location for Qt library?

I am new to qmake and I am trying to build an existing application. Qt was originally installed in /usr/local/lib/Qt-4.3.5 and 'qmake -query QT_INSTALL_PREFIX' returns that path.

I have moved the Qt library to another location and the generated Makefiles are peppered with the /usr/local original path.

How can I force qmake to use the new location I selected without recompiling Qt?