PG&E Corp. shares tumbled after the company said it has fully drawn down revolving credit facilities, raising the specter of bankruptcy as wildfire losses grow.

The parent company and its utility subsidiary now have a total of $3.46 billion in cash and cash equivalents after drawing down revolving credit facilities, according to a regulatory filing Tuesday. Damages from the deadly Northern California wildfire may reach as much as $15 billion, Citigroup Inc. analyst Praful Mehta wrote in a research note Wednesday.

“The risk of bankruptcy is very real for these guys,” Bloomberg Intelligence analyst Jaimin Patel said in an interview....