Fletcher Building, New Zealand's largest building company, is donating $1 million to help those who suffered losses in the Canterbury earthquake at the weekend and to help the recovery.

The donation was announced this morning by chief executive Jonathan Ling.

The company was working through the most appropriate way for this support to be delivered, he said.

Fletcher Building said its businesses in the Christchurch region all escaped without significant damage or injury to employees.

All businesses were expected to be fully operational in the next few days.

Other corporate donors include TelstraClear, which has given $100,000 to the Christchurch Restoration Fund established by Mayor Bob Parker, and the BNZ, which has established a $1 million relief programme that includes a $250,000 donation to the Red Cross, $250,000 to the Salvation army, plus assistance to staff and customers.

Fonterra has donated $1 million to the mayor's Restoration Fund.

Telecom has made all payphone calls free in the Christchurch area free for local, national and mobile calls.

As of 11.30am this morning, more than 1000 calls had been placed via the free service, the company said.

Many smaller businesses are also chipping in, including Auckland social media darling Giapo, which is donating 20% of today's turnover to the Christchurch City Mission, and deal site grabone.co.nz, which has donated $5000.

Charities collecting money for the quake-struck city include The Red Cross and the Salvation Army.

Volunteers for the earthquake clean-up effort can call the Christchurch City Council on 0-3-941 8999. See more information for volunteers on the council's website here.