One person has been seriously injured in an accident in rural Canterbury tonight.

St John said three of its vehicles attended a "traffic incident" at the Waimakariri River about 8pm.

A patient was taken to Christchurch Hospital.

About the same time, the police received reports of a person coming off a motorcycle at a stopbank, or riverside flood barrier, near Swannanoa, 35km northwest of Christchurch.

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The Christchurch-based Westpac rescue helicopter was still at the scene about 9.15pm, a spokesman said.

"There is shingle road access to it but if a person is seriously [injured] they'll call for a helicopter."

The spokesman said the area was a popular trail-bike riding spot.

The helicopter was believed to be near the river's north bank, near Diversion Rd.