Tourists from mainland China board a train at the Lo Wu border control point in Hong Kong on May 1, 2024 at the start of the Golden Week holiday period. Peter Parks, AFP 

Hong Kong last month recorded its hottest April since meteorological records began in 1884, according to the city's weather observatory.

Last month's average temperature of 26.4 degrees Celsius (79.5 degrees Fahrenheit) in Hong Kong made it "the warmest April" since records began 140 years ago, the observatory said on Wednesday.

"Summer is not yet here but April was already record-breakingly hot," the observatory announced on social media.

The subtropical Chinese city has faced extreme heat in recent years, with dozens of high-temperature records, including daily and monthly highs, set annually since 2019, observatory data showed.

On April 27, Hong Kong also set daily temperature records for April, including the highest daily average of 28.8, and the highest daily low of 27.7.

In contrast, between 1991 and 2020, the average daily temperature in April was between 21.1 and 25.6.

The record-warm April this year came after an "exceptionally warm" winter from December to February, and a "much warmer than usual" March, with the observatory expecting "above normal" temperatures throughout 2024.

Hong Kong's labour department on Wednesday updated its three-tier warning system for heat stress at work, pegging it to the observatory's hot weather alerts and doubling the minimum duration of a heat advisory from 30 minutes to one hour.

The system mandates rest periods or suspension of work depending on temperature levels and types of work.

Hong Kong has not included heatstroke as a work-related injury in its laws despite reports of people dying from the illness while working in sizzling summer heat.

The labour department's heat stress warning system was rolled out last year. Critics said it adopted an overly high threshold for issuing warnings and could not hold non-complying employers legally liable.

Globally, scientists warn extreme heat will become more frequent and intense because of human-induced climate change.