Zimbabwe's President Robert Mugabe has read out the wrong speech at the opening of parliament.

He gave the same one during his state-of-the-nation address on 25 August, when he was heckled by opposition MPs.

His spokesman told the state-run Herald paper the error was because of a mix-up in the president's secretarial office.

The BBC's Brian Hungwe in Harare says tensions were high ahead of the speech and the state broadcaster cancelled its live feed fearing further disruptions.

At least six MPs from the opposition Movement for Democratic Change (MDC) received a text message from a sender called "Death" warning them to behave.

"Warning: Immunity ends in parliament... act wisely by not disturbing the proceedings of parliament," the message on opposition MP Nelson Chamisa's phone said.

Before the 91-year-old president spoke, the parliamentary speaker also warned against disrupting proceedings.

After Mugabe began speaking, it was not long before it dawned on those present that they had heard it all before, our reporter says.

But during the speech, the MDC members sat quietly, while ruling Zanu-PF party supporters clapped at regular intervals, Reuters news agency reports.

The president made reference to the country amending labour laws to protect workers from arbitrary termination of employment, efforts being made to stimulate investment and the country registering modest growth in tourism and agriculture, our correspondent says.

The first time Mugabe read the speech opposition MPs sang protest songs against his 10-point plan to solve the country's economic crisis.

Presidential spokesman George Charamba said the error in delivering the wrong speech was "sincerely regretted".

He added that the president would read the correct speech later at a hotel in the capital Harare, Reuters reports.