The northbound lanes of the Interstate 35 lower deck are closed near 34th Street after debris fell into the roadway from the upper deck.

The Texas Transportation Department said a bridge rail had been stuck in a crash and that it was cleaning the area. "All lanes will open as quickly as possible on both decks," TxDOT said in a tweet.

We confirmed bridge rail was struck due to a crash. We are cleaning area to ensure no loose concrete is present. Warning signs & barrels will alert drivers & barricade area; repairs will be made in coming days. All lanes will open as quickly as possible on both decks — TxDOT Austin (@TxDOTAustin) August 21, 2019

Drivers should expect traffic delays and avoid this section of I-35, just south of 38th 1/2 Street. TxDOT said the lower deck should be open again by Wednesday morning.

The Austin Police Department initially said in a tweet shortly before 8 p.m. that “large pieces” of the upper deck fell onto the road below. It later said it wasn't sure where the debris was from.

Update on I-35: TXDOT is on scene assessing where the chunk(s) of concrete came from and how it may have happened. The upper deck is not falling down and is open. The lower deck is closed while the engineers assess it. APD PIO is not responding. — Austin Police Dept (@Austin_Police) August 21, 2019

There was no mention of injuries.

• I-35 traffic cams

This post has been updated. This is a developing story.