Police responded to the incident on Main South Rd (SH1) after reports the tractor had run into trouble on the north lane of the bridge about 11am.
The tractor was removed and the northbound lane of the bridge reopened about 1.20pm.
Waka Kotahi NZ Transport Agency said about 12.15pm a line of traffic stretched from the bridge to Pendarves Rakaia Rd, south of Rakaia, and the southbound queue was to Breadings Rd.
"Road users should still expect delays until all congestion has been cleared," a Waka Kotahi spokesperson said.