Bersatu leaders have fired back at Johor Umno chief Hasni Mohammad for suggesting Pakatan Harapan's 66-year-old candidate for the Tanjung Piai by-election may kick the bucket.

Hours after Harapan named Tanjung Piai Bersatu chief Karmaine Sardini as its candidate for the by-election, Hasni said he hoped that another by-election would not have to be called if the Bersatu politician wins.

"Hasni's statement was insolent and unacceptable," said Bersatu Youth executive council member Mohd Fahim Mohd Farid said in a statement today.

He added that age is not a limitation as Prime Minister Dr Mahathir Mohamad is 94 years old and still able to serve the country, sometimes better than those who are younger.

"In the end, it is about the spirit and intent to serve the people and not about age," he said.

Meanwhile, Johor Bersatu secretary Mohd Solihan Badri said the issue of life and death is not for people to decide.

"Do not speak as such for it is Allah who determines how long we live. Even the young can die.

"Let us ensure Harapan's candidate can win and continue Farid's legacy," he said in a separate statement.

The Tanjung Piai by-election was called following the passing of its incumbent MP Mohd Farid Mohd Rafik.

Bersatu's Farid, who was a deputy minister in the Prime Minister's Department, died from a heart attack last month.

In the last general election, he wrested the parliamentary seat from MCA's Wee Jeck Seng by only 524 votes.

BN has yet to announce its candidate, as Umno and MCA are allegedly still negotiating which party should represent the coalition in Tanjung Piai.

The candidates will formally be nominated on Nov 2, while Tanjung Piai voters are scheduled to go to the polls on Nov 16.