HYDERABAD, Pakistan (Reuters) - Pakistani Prime Minister Nawaz Sharif on Friday inaugurated one of the first highway sections of his government's planned $11.5 billion spending plan on roads intended to expand trade and speed up economic growth.

Sharif gave a speech and then drove in a convoy down part of the new 75-km section of the Karachi-Hyderabad Motorway (M-9) he dedicated on Friday as part of a planned network connecting the southern port city of Karachi to interior cities.

Pakistan is embarking on the biggest road-building program in its history, with Sharif's office saying projects worth 1,200 billion Pakistan rupees ($11.5 billion) are under way.

"After the completion of these projects, the total length of (new) motorways will reach 2,000 km," Sharif's office said in a statement.

Pakistan's national network of highways now stretches to about 12,000 kms, according to the National Highway Authority.

Many of the new projects are slated to link up with roads connecting to the wider $57 billion China-Pakistan Economic Corridor, a Beijing-funded project building dozens of roads, ports and power plants in Pakistan.

($1 = 104.7500 Pakistani rupees)

(Writing by Kay Johnson; Editing by Hugh Lawson)