UPDATE: 11:39 a.m.
The California Highway Patrol is reporting that all lanes are now open.
UPDATE: 11:16 a.m.
CHP is reporting the number 1 and 2 lanes are now open at the eastbound transition to the northbound I-215.
UPDATE: 10:37 a.m.
The fully loaded tractor trailer is on its side blocking all eastbound lanes, the CHP reported.
Lanes are expected to closed for at least one hour until the big rig is upright, according to CHP.
UPDATE: 10:30 a.m.
A Sig Alert has been issued. CHP does not have an estimate when it will be lifted.
The driver was seen walking around, according to the CHP, but it was not immediately clear if he was injured.
CHP is urging caution to motorists stuck in traffic after reports of vehicles using the center divider and the right shoulder to pass.
An overturned big rig has prompted the closure of the eastbound Riverside (91) Freeway at the state Route 60 interchange, according to the California Highway Patrol.
The crash was reported at 9:13 a.m. on the 91 Freeway at the state Route 60 and 215 Freeway interchanges, according to the California Highway Patrol.
Traffic is being diverted to the southbound 215 Freeway.
City News Service contributed to this report