The search for a missing man who jumped into the sea to rescue two children is set to resume this morning.

The man, 33, entered the water to help the youngsters, aged three and 17, who had got into difficulty close to the entrance of Portsmouth Harbour yesterday afternoon, Hampshire Constabulary said.

Both the toddler, the youth and another man who dived into the sea to help with the rescue made it safely to dry land.

But it is believed the missing rescuer, who was last seen close to the harbour entrance, may have been dragged under the surface by strong currents.

A search operation involving lifeboats, a Coastguard helicopter, Ministry of Defence police boats and a Coastguard rescue team was launched shortly after the incident at 3.40pm.

The coastguard teams temporarily called off their search at about 10pm last night due to bad light, but will resume the operation this morning, the Maritime and Coastguard Agency said.

An agency spokesman added: ''Solent Coastguard received a call at 3.40pm yesterday to reports that four people were struggling in the water.

''Three of them were quickly rescued, but the fourth was not recovered from the water.

''The Hillhead and Portsmouth Coastguard rescue teams, the Coastguard helicopter based at Lee-on-Solent, two Gosport independent lifeboats, two Portsmouth RNLI lifeboats, two MOD police launches, Royal Navy personnel, police, fire and rescue officers and ambulance crew searched through the evening but the missing man was not found.''

A smaller scale search involving coastguard rescue officers will begin at sunrise, he added.

A Solent Coastguard spokeswoman said she did not know whether any of the people involved in the incident were related to one another.

''The man was last seen in the water close to the Square Tower which is pretty close to the harbour entrance,'' she added.

''There are very strong currents, deep channels, ferries in and out and all sorts of traffic.''

A woman working at The Wellington pub, who did not wish to be named, said the incident had happened on the beach across the road. She said she believed the older man had swum out to sea to rescue two boys who were in distress.