* Wuhan official says residents should stay home
* China to observe national mourning for coronavirus "martyrs"
* Mainland reports 31 new infections, down from 35 a day earlier (Adds schools to reopen, foreign diplomats, Henan case; paragraphs 12,18-21)
By Brenda Goh
WUHAN, China, April 3 (Reuters) - The top official in China's coronavirus epicentre of Wuhan warned residents to stay vigilant and avoid going out, even as the latest data showed a decline in new cases in the mainland and no new infections in the central city.
The country where the virus emerged late last year will observe three minutes of silence nationwide on Saturday to mourn the thousands of "martyrs" who died in the fight against the pandemic, the official Xinhua news agency said.
Air raid sirens and the horns of automobiles, trains and ships will "wail in grief" after the silence, to be observed at 10 a.m. (0200 GMT), it added.
China appears to have curbed the epidemic with draconian curbs that paralysed the world's second-biggest economy for two months.
On Friday, the National Health Commission reported 31 new cases, down from 35 a day earlier and dramatically lower than February's peak. All but two involved travellers from overseas.
Total infections on the mainland, a figure that excludes asymptomatic patients, stand at 81,620, while the death toll rose by four to 3,322. Worldwide, the number of cases has topped 1 million, with at least 52,000 deaths.
Beijing has pushed industries to return to work as the epidemic eases, hoping for a quick recovery from what many analysts expect to have been a deep contraction of China's economy in the first quarter.
Top officials, however, are concerned about the risk of a second wave of infections.
The threat of a rebound in Wuhan remains high, said Wang Zhonglin, chief of its Communist Party, ordering residents to avoid leaving their homes unless necessary.
The comments came about two weeks after officials eased the city's total lockdown, allowing some of its population of 11 million to go outdoors for the first time since Jan. 23, though they were still not able to leave Wuhan.
The capital of Hubei province has been the hardest hit by the virus, with 50,007 cases reported. From April 8, it is due to allow people to travel outside the city, where volunteers in hazmat suits have been spraying disinfectant.
Schools are starting to reopen in the eastern provinces of Zhejiang and Shandong, authorities said on Friday. Some Zhejiang students will return on April 13, and others in Shandong on April 15.
However, some areas have gradually reimposed curbs, including the closures of cinemas allowed to re-open.
On Wednesday, a county in the central province of Henan banned people from leaving without proper authorisation and confined residents to homes unless they had clearance, following several infections in the area.
Local health authorities have also been ordered to step up detection, monitoring and supervision of infected patients who showed no symptoms.
Wuhan alone reported 51 new asymptomatic cases and said 705 people with the virus but without symptoms were under medical observation.
Beijing has indefinitely banned entry by foreigners to hold down cases involving overseas travellers, though it has chartered planes to bring home citizens from countries with severe outbreaks.
On Friday, the foreign ministry said it was advising foreign diplomats not to come to Beijing, following the emergence of infections among some of them in China.
"We recommend in the near future that diplomatic missions in China suspend people returning to Beijing or rotations," said spokeswoman Hua Chunying, adding that the measure aimed purely at epidemic prevention and control.
China is also stepping up a crackdown on outbreak-related offences. A court in Henan jailed a recovered patient surnamed Guo for 1-1/2 years on Friday, for lying to authorities about his travel history in Italy, Xinhua said.
Guo was the province's first imported case from abroad. (Reporting by Brenda Goh in Wuhan and Ryan Woo, Lusha Zhang and Gabriel Crossley in Beijing; Writing by Se Young Lee; Editing by Stephen Coates and Clarence Fernandez)
Our Standards: The Thomson Reuters Trust Principles.