Steve Smith made another century but Australia and Pakistan look certain to play out a draw after rain again interrupted the second Test.

The Australia captain was unbeaten on 100 when rain led to an early close of play at the MCG on Thursday.

Storms in Melbourne meant the hosts finished day four at 465-6, holding a lead of just 22, with Mitchell Starc (7) also unbeaten at stumps.

Australia hold a 1-0 lead in the three-Test series, and clearer weather is expected on Friday.

Resuming at 278-2, the hosts were dealt an early blow as Usman Khawaja (97) chased a Wahab Riaz (2-135) delivery outside off and edged behind to Sarfraz Ahmed.

Peter Handscomb, who has made a fine start to his Test career, raced to 50 off just 69 balls, bringing up his half-century with a boundary to fine leg.

The new ball brought an opportunity for Pakistan, but Mohammad Amir (0-74) put down a tough return chance off Handscomb.

Handscomb would depart for 54, his thick edge off Sohail Khan (2-86) caught at point by Sami Aslam.

Amir was the unluckiest of the bowlers as Smith reached 50, before the under-fire Nic Maddinson (22) did little to ease the pressure on him.

The left-hander came down the pitch to Yasir Shah (2-150) and was clean bowled.

Azhar Ali was then involved in a frightening incident, struck hard on the helmet at short leg by a Matthew Wade pull shot.

He appeared to be OK as he walked off the field.

Wade (9) fell soon after, edging to Asad Shafiq at first slip off Sohail.

Smith brought up his century off what proved to be the second last ball of the day, cutting Sohail for three for his 17th Test ton.