A NSW MP has urged Prime Minister Scott Morrison to call an early election and get "smashed" at the polls in order to save bigger losses at the state level.

Peter Phelps' comments come after the Liberals' historic loss of Malcolm Turnbull's seat of Wentworth to independent Kerryn Phelps on the weekend. The result means the government has lost its one-seat majority, which Mr Morrison conceded was due to his predecessor's ousting in August.

Dr Phelps, a former staffer to seven federal Liberal MPs and a member of the NSW Legislative Council, was responding to Newspoll analysis showing a significant slump in support for the federal Coalition across the five major states.

He said Mr Morrison should sacrifice the federal Coalition to give state Liberals a chance.