Labor has kept its lead over the Coalition in a tightening race for the May 18 election, with a new poll showing it is ahead by 52 to 48 per cent in two-party terms despite losing some of its support.

The exclusive Ipsos poll for The Sydney Morning Herald and The Age finds the Coalition has gained ground during the election campaign to boost its support from the result of 53 to 47 per cent one month ago.

But Prime Minister Scott Morrison is under significant pressure on his leadership and performance ratings, with voters marking him down over the past month and turning towards Opposition Leader Bill Shorten.

While 45 per cent of voters name Mr Morrison their preferred prime minister compared to 40 per cent for Mr Shorten, the gap between the two leaders is the closest it has ever been.