A rollover crash involving two vehicles occurred on East Grant Road and North Alvernon Way, authorities said.
Two people were treated by Tucson Fire Department paramedics and both were taken to a hospital, said fire Capt. Andy Skaggs, shortly after 4 p.m.
One person is in critical condition, Skaggs said.
He said one of the vehicles involved is a taxi-cab.
Motorists are asked to avoid the area.
No further information is immediately available.