Aug 12 (Reuters) - Food-delivery firm DoorDash Inc's loss widened more than expected in the second quarter as the U.S. upstart spent heavily to expand internationally and into a crowded market for grocery during the pandemic.

The company said on Thursday its total expenses more than doubled to $1.34 billion, overshadowing a surge in revenue and sending its shares down 5% in extended trading.

Demand for delivery of essentials has stayed strong during the health crisis, leading DoorDash to sign new partnerships with pet specialty retailer PetSmart Inc, grocer Albertsons Inc and plant-based meat maker Beyond Meat Inc.

The company has also increased its presence outside its core market of the United States by expanding into Canada, Australia and Japan.

While that helped the company beat revenue expectations with an 83% surge to $1.24 billion, its loss of 30 cents per share was wider than a Refinitiv IBES estimate of a 20 cents loss.

The company said it expects full-year marketplace gross order value - a metric measuring the total value of all app orders and subscription fees - between $39 billion and $40.5 billion. It had forecast $35 billion to $38 billion earlier.

It also raised its outlook for core earnings. (Reporting by Mehr Bedi and Praveen Paramasivam in Bengaluru; Editing by Devika Syamnath)