Travel alerts were issued after New Zealand’s South Island was shaken by a powerful earthquake hours after an initial quake killed two people.

The new 6.3 magnitude tremor struck at 1.45pm local time at a depth of six miles, north-east of Christchurch.

This followed a 7.5-magnitude quake, with the same depth, which hit the same area shortly after midnight, triggering tsunami warnings.

Hundreds of strong aftershocks caused power shortages and cuts in water supply since the initial quake.

Air New Zealand warned of possible travel disruption due to a “series of major earthquakes,” with its contact centre experiencing a high volume of calls.

The airline said: “If your travel is not urgent, or you wish to defer to a later date of travel, you do not need to phone urgently and can call at your own convenience any time this week.”

The carrier relaxed certain restrictions for passengers wanting to alter their travel arrangements but said normal refund rules would still apply. 

A large river clogged up by a landslide breached its banks sending a “large wall of water” downstream.

Residents around the Clarence River – one of the largest on South Island – were being urged to move to higher ground.

Waves of around 6.6ft hit the east coast shortly after the first earthquake. Authorities have since lifted the tsunami alert, but are still warning people to stay away from the shoreline.

The popular tourist destination of Kaikoura saw its main road blocked by landslides, with telecommunications, water and power supplies cut off.

The Foreign and Commonwealth Office said: “A tsunami warning has issued for coastal areas following a series of large earthquakes in the Marlborough and Canterbury areas of South Island shortly after midnight local time on Monday.

“The New Zealand Ministry of Defence and Emergency Management has issued a tsunami warning for he eastern coast of north and south island including the Chatham Islands and is advising those in affected coastal areas to move inland or to higher ground immediately.”

Christchurch is still recovering from a 2011 earthquake that killed 185 people and destroyed the city centre.

Tourism New Zealand said the damage had affected mainly rural areas, and that all airports were open and operational.

“Much of New Zealand remains unaffected. It appears the greatest impact is in rural North Canterbury, Kaikoura and Wellington, although information is still being confirmed,” a spokesman said. “If you have clients who are booked to travel to New Zealand, or enquiring about future travel plans, you should first check the Home Office for travel advice.”

Members of the public concerned for the safety of friends and family have been encouraged to contact the British High Commission in Wellington.