Ashlee Simpson says there is "plenty of time" before her sister gives birth.

The 27-year-old star was in Australia celebrating the opening of nightclub Marquee The Star, as her older sister Jessica Simpson prepares for the arrival of her baby in the US.

Ashlee attended the event in Sydney last Thursday with former brother-in-law Nick Lachey and his wife Vanessa, Joe Jonas, Kellan Lutz, Wilmer Valderrama and Minka Kelly.

Jessica is a few weeks away from giving birth to her first child with fianc Eric Johnson.

But Ashlee, who is mother to three-year-old boy Bronx, is not concerned she will miss seeing the baby come into the world.

"I have plenty of time," Ashlee told Us Weekly. "And I'm going home [today] so it will be fine."

Last week, 31-year-old Jessica was overheard telling a shopper at Fred Segal she has one month left to go.

She has been happy to speak publicly about her pregnancy including the sex of the baby and her delivery fears.

The singer-and-actress recently revealed she is worried about her waters breaking as she has so much amniotic fluid. The size of her baby bump has left some fans astounded.

"I feel I have a bowling ball sitting on my hoo hah!" she told talk show host Jimmy Kimmel.

"Apparently I have a lot of amniotic fluid, so whenever my water breaks it will be like a fire hydrant!"

The Fashion Star mentor is reportedly spending $2 million around the time she gives birth to her first child to make sure everything goes smoothly.

According to In Touch she is spending $500,000 on a birthing suite, $100,000 on food and room service, $14,500 on a crib and nearly $70,000 on a private jet for a possible trip back home to Texas.