Immigration officials on Thursday said they expect Lo Wu will be the busiest border crossing during the mainland's "Golden Week" holiday next week.

On Tuesday, Chief Executive John Lee projected almost six million arrivals and departures for the week, with some 800,000 mainland tourists expected to come to Hong Kong.

The Immigration Department said Labour Day on May 1 is tipped to be the busiest day, with arrivals and departures reaching one million at land checkpoints.

It said that between April 30 and May 5, an average of around 200,000 rail journeys a day are expected through Lo Wu, and 170,000 via Lok Ma Chau.

An average of 130,000 journeys a day are expected for the bridge to Zhuhai and Macau.

The Immigration Department's boundary division commander, Ng Hoi-ka, said travellers are advised to use the department's mobile app for real-time border traffic information, so they can see how busy the different checkpoints are.

She also called on travellers to avoid crossing the border during peak hours.

"If all travellers cross the border during the peak hours at the same time, there's bound to be some congestion and longer waiting times. So we urge everyone, if you can, please avoid the peak hours," she said at a press briefing.

"Generally speaking, for departures, it starts getting crowded from eight in the morning, and it'd be the busiest between 10 and 12 o'clock."

She added that her department has prepared for the busy week by curbing holidays for frontline officers.

A control centre will be set up along with other departments to monitor checkpoint operations, so officers can respond to any emergencies.