Leaked National Party emails show its MPs are divided over John Key's flag change and that a crisis meeting of MPs has been held to give the campaign a boost.

An email obtained by Newshub shows that only 32 out of 59 National MPs were invited to a meeting about changing the flag today -- meaning about 54 percent of Mr Key's Caucus is in support.

The email follows a Caucus meeting yesterday where the flag was discussed.

It was sent to the following list of recipients: