A grass fire at Wellington's historic cricket ground, the Basin Reserve, caused traffic jams through the central city.

By 1.50pm, the flames running up by the Basin's outer fence had been put out and two fire crews were dousing flame-retardant foam on the plants to dampen down the fire. With the four lanes at the north-east corner of the road system reduced to two, Sunday traffic had backed up past The Terrace tunnel and onto the motorway.

The fire broke out on one of the grounds' banks shortly after 1.30pm, Fire Service senior station officer Simon Johnson said.

RACHEL SIMMERS Flames move along the grass bank at the Basin Reserve.

"There would have been a lot of smoke and a lot of flames. We were getting multiple calls about it. You could see it from the traffic cameras monitoring the tunnel."

The cause of the fire was not yet known, but nothing suspicious had been found. "We'll try and find out, but it's difficult to say."

The fire crews hoped by 2.30pm the job would be complete and they could reopen the closed lanes.