Reviewers of Apple Inc's latest smartwatch unveiled a week ago were impressed by some of its smartphone features, but  several said on Wednesday they did not recommend the device because of connectivity problems and poor battery life.

The Watch Series 3, which starts at US$399 and was launched alongside new iPhone models, boasts features that now work without an iPhone nearby such as email, messaging, smart home controls, maps and Siri.

Mashable's Lance Ulanoff dubbed it the "smartest smartwatch yet" as it allows users to do many of the things that they do with their iPhones.

However, the watch's standout feature - which allows users to make calls without an iPhone - has turned out to be a cause for concern due to a connectivity glitch.

"Considering that my Apple Watch Series 3 with LTE (both first and second review units) didn't function like it was supposed to, I can't recommend buying it - and paying the monthly cell fee - based on promises," Verge reviewer Lauren Goode wrote.

Apple said the watch can experience LTE connectivity problems when it connects to open wi-fi networks the user has visited before, such as at a hotel or a coffee shop.

The company is "investigating a fix for a future software release," Apple spokeswoman Amy Bessette told Reuters.

Apart from connection issues, some reviewers were disappointed with the drain on the watch's battery while making calls. Apple had touted up to 18 hours of battery life but said the watch would get only one hour of battery life on a cellular phone call.

The Wall Street Journal's Joanna Stern wrote that users "should all hold off until, say, Series X," referring to the latest iPhone X model number.

The mixed reviews weighed on Apple shares, which were down about 2 per cent at US$155 in afternoon trading. Gene Munster, a longtime Apple analyst with Loup Ventures, doubted issues with the Series 3 Watch would hurt Apple's bottom line. "That review takeaway is a negative but is not a surprise. This is the first generation watch with LTE," he told Reuters.

Apple also experienced hiccups with iOS 11, the new operating system the firm released Tuesday.

For business users, iOS 11's Mail application had problems sending mail for Microsoft Exchange and Outlook.com mail accounts.

"We're working closely with Microsoft to resolve the issue and will release a fix soon in an upcoming software update," Apple spokeswoman Trudy Muller told Reuters.