The underpass of the Nimitz Freeway at 7th Street in West Oakland was completely flooded Thursday morning, creating a striking body of standing water on the neighboring frontage road that was visible from BART.

Oakland police were seen blocking off the underpass shortly before 8 a.m.

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Although the underpass was closed, on the adjacent flooded frontage road, many cars could be seen driving through after some hesitation.

It was difficult to tell the depth of the water on the frontage road, but it was deep enough that smaller sedans could be seen with water splashing onto the hoods of their cars. Larger trucks had a less difficult time getting through.

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A Caltrans employee on the scene said there was no estimated time of reopening for the underpass.

AC Transit rider Erica Joy tweeted a view of her commute through the area. As the bus drove into the flooded frontage road, water sloshed onto bus and riders lifted up their feet to avoid getting wet.

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"My bus just went through a whole ass lake. the bay area doesn't do rain well," Joy jokes in the tweet.

SFGATE has reached out to Caltrans for more information and will update when we hear back.

Alix Martichoux and Filipa Ioannou are SFGATE staff writers. Email amartichoux@sfchronicle.com and fioannou@sfchronicle.com