A car hire company drew the ire of New Zealand Prime Minister John Key Wednesday for charging a tourist family for being unable to return their car after their sons were crushed by glacier ice.

Ashish Miranda, 24, an aerospace engineer and his student brother Akshay, 22, were crushed beneath 100 tonnes of falling ice as they posed for photos at the base of Fox Glacier on the South Island west coast last Thursday.

Ashish's body was recovered hours after the accident but the danger of more ice falls has prevented the recovery of Akshay, who had the keys to the hire car in his pocket.

Hire car company New Zealand Car Rental Specialists has demanded the brothers' parents, who were travelling with their sons, pay up to 1,950 dollars (1,085 US) to replace the keys and have the car towed back to the capital Wellington.

Prime Minister Key said the company should have shown more compassion to the family, who live in Melbourne.

"Quite frankly they may have a legal point but sometimes businesses should look beyond their legal obligations to recognise that this was a tragic loss of two Australians," he told reporters.

"To be out there effectively charging their families now for the lost keys is crass at best and probably truly bad business practice."

New Zealand Car Rental Specialists owner Edwin Chan said he refused to waive the towing fee because he still had to pay to replace the keys and have the car towed.

He told the New Zealand Press Association his company had waived other expenses, including for late return of the car.

Radio New Zealand reported that a business owner from the tourist centre of Queenstown had offered to pay the money owed by the family to the car hire company.