A spokesman for Vector said crews onsite were unable to start work on the damaged transformer while the serious crash unit investigates.
"As a result, we're not able to confirm the number of customers impacted," spokesman Matthew Britton said.
"Our crew will stand by until we're able to access the site again and will continue to evaluate options for redirecting the flow of power to restore some customers if possible."
Pictures from the scene of the crash show a BMW car crashed into the transformer, where it came to a stop.
The back window and rear taillight of the car were broken and the fence beside the footpath and ground ripped up.
"Network equipment should always be treated as live, and if they see them damaged or down following incidents like this," he said.
If anyone comes across damaged power equipment they are advised to keep clear and contact Vector on 0508 VECTOR.
BUCKLAND RD, MANGERE - ROAD CLOSED - 3:00PM Due to an earlier crash, Buckland Rd is CLOSED between Lyncroft St and Wickham Way. Expect delays and avoid the area if possible. ^TH pic.twitter.com/Z894lgKYfh