SINGAPORE - SingTel has begun doubling the speed of its 4G networks, with the first site at Singapore Expo and now offering mobile broadband speeds of up to 300Mbps.

M1 has also doubled the speed of its 4G network to 300Mbps in selected locations in Orchard Road and Jurong.

Nationwide upgrade is expected to be complete by the end of this year for M1 and next year for SingTel. The upgrade will come at no additional charge for their existing 4G customers, but The Straits Times understands that handsets that support this speed are not available at present.

The first compatible device, a Huawei dongle, will be available in mid-July, said SingTel. Smartphones and tablets are expected to be available soon after, it added.

Meanwhile, StarHub's 4G network speed will be doubled to 150Mbps from July, and further upgraded to 300Mbps later this year.

SingTel also said its Singapore mobile users will be able to roam on a 4G network in China for the first time. For $20 a day, the DataRoam Saver service offers unlimited 4G data usage via SingTel's partner China Mobile, the country's largest mobile operator.

Mr Johan Buse, SingTel's vice president of consumer marketing, said: "As the second most popular destination for Singapore travellers, China is an important addition to our global 4G roaming network."

The service is currently only available for iPhone 5S and 5C smartphones. Other handsets will be supported in the coming months.