Qualcomm has demonstrated mobile internet speeds of 1Gbps using a 5G smartphone chip.
The chipset manufacturer claims this is the first working 5G data connection on a mobile device.
The fifth generation of the mobile network does not yet exist, but it promises faster data speeds and more bandwidth to carry more web traffic.
Qualcomm is describing the demonstration as a "major milestone", but one expert is playing it down.
1Gbps is equivalent to 1,000Mbps, and this speed would enable you to download a one-hour TV programme in HD from BBC iPlayer in less than six seconds.
"It's not a big deal," Prof William Webb, a independent consultant and author of the book The 5G Myth: When vision decoupled from reality, told the BBC.
"5G is not yet clearly defined, they've just postulated what they think it will look like.
"It's not 5G in its final form, so it's premature to say it's a 5G demonstration."
Prof Webb added that speeds higher than 1Gbps were already achievable on 4G.
For example, Huawei's Kirin 970 chipset offered mobile speeds of up to 1.2Gbps when used with compatible network equipment.
Qualcomm said the demonstration, at its laboratories in San Diego, had used its first dedicated 5G chip, the Snapdragon X50 NR modem chipset, on the 28GHz millimetre wave spectrum band.
"This demonstration... was only the first data connection on this 5G mode," said a spokesman for the firm.
"When it is finished and ready to ship to smartphone makers, it will be capable of 5Gbps speed, which no 4G LTE chip currently available can support.
"What our announcement represents is the first steps we are taking to counter sceptics like Prof Webb: yes, millimetre wave 5G is a viable technology for mobile devices and networks, and our achievement proves the steady progress we are making."
What is 5G?
Today's 4G mobile networks currently make use of the sub-6GHz frequencies, but these are now heavily crowded.
Mobile operators are running out of capacity to carry the huge amounts of web traffic generated by consumers on billions of mobile devices, in addition to data being sent from internet-enabled sensors in smart devices.
The specifications for 5G have not yet been set out by the global mobile standards body, 3GPP, so various parts of the industry are trying different technologies, with the hope that 5G will be ready by 2019.
Some of the technologies involve optimising the current 4G network by making the transit of data more efficient, in order to offer greater capacity and higher speeds.
But there are also plans to make use of the currently unused 28GHz and 39GHz millimetre wave spectrum bands, which are found in the electromagnetic spectrum between microwaves and infrared waves.
Millimetre waves offer far more bandwidth than the sub-6GHz frequencies, but the radio signal deteriorates if data is transmitted over more than a few kilometres.
"There are many different definitions of 5G, some of which could be implemented by 2019, and those that wouldn't be, such as millimetre wave, which will probably take a lot longer," said Prof Webb.
Qualcomm takes issue with this analysis, saying that it aims to have millimetre wave-capable smartphones in users' hands before July 2019, when it expects the first compatible networks to have become available.