Railway enthusiasts reported queueing all night to be part of history as the first ever service on the cross-harbour section of the MTR's East Rail Line departed early on Sunday morning.

Some people joining the service at the new Exhibition Centre station said they'd joined the line at 10pm on Saturday to guarantee a place on the first train.

MTR executives and guests were also aboard the train, which made its way beneath the harbour to Hung Hom in just five minutes.

The 46 kilometre line connects the northeastern New Territories with Hong Kong Island for the first time.

At an opening ceremony on Saturday, Chief Executive Carrie Lam predicted that the line would be an immense success and said it may even be extended as far as Shenzhen in future.