Amazon's cloud business is just getting started, according to one Wall Street firm.

D.A. Davidson increased its price target for Amazon shares to $1,800 from $1,500, representing 33 percent upside to Wednesday's close. It's the highest target out of the 42 analysts who cover Amazon, according to FactSet.

"We see two potential catalysts for shares over the next 12-month period: stronger-than-expected operating results from the company's cloud computing efforts, which we believe remains the primary driver of its share price and 2) due to its increasing mix of highly-profitable third-party sales (which surpassed 50% for the first time in 2Q17)," analyst Tom Forte wrote in a note to clients Thursday.

The firm also reiterated its buy rating. If Amazon's stock reaches Forte's $1,800 forecast, the company's market value would be nearly $870 billion.

Amazon's shares were up slightly Thursday. The company reports fourth-quarter earnings next Thursday.

— CNBC's Michael Bloom contributed to this story.